Sign in with
Sign up | Sign in
Picking The Right Power Supply: What You Should Know
By ,
1. Brought To You By Granny’s Radio

This piece is for the folks who'd like to learn more about about the facts, technologies, and terminology behind PC power supplies.

Keeping The Explanation Simple

Don't worry; this won’t be complicated or boring. We’ll just quickly explain how a switching PSU works, then use examples to illustrate some of the most common technical issues. We’ll explain what efficiency, loss, and reactive power mean, and why those words are relevant to you. Then we’ll look at the possible and (more importantly) necessary protective measures before applying theoretical knowledge to practical examples.

Practical Examples

Big versus small, efficient versus high-performance; we're going to examine three different PCs based on a trio of different usage models, calculate the power supplies they really need, and then explain the right class of PSU to use in them based on quality and long-term environmental impact.

The Frequency Trick

Remember those ancient radios with the vacuum tubes? They were massively built and tended to be clunky, heavy, very functional-looking things. However, it wasn’t just the wooden frame contributing to their weight. The large, massive transformers added their part as well.

The point is, even back then, clever engineers were taking advantage of a neat trick of physics that would later come to be used in every modern switching power supply. In order to convert a high alternating current into a low one and achieve galvanic separation of currents, they used normal, albeit powerful, transformers with a core made of iron plates.

While a mains frequency of 60 Hz required a comparatively large transformer, the so-called output transformers that delivered much higher low-frequency signals between 100 Hz and 16 kHz could be built much smaller while handling the same power. By aggressively capping the frequencies at the lower end of the spectrum, it was possible to increase the power that could be handled by a transformer of the same size. With the invention and subsequent introduction of new components, such as powerful switching tubes, and later, semiconductors using the same underlying physical principle, this advantage was carried over into other fields, opening up new possibilities.

And How Does That Apply To My PC?

Due to the high overall power requirements of modern computers, a conventional transformer-based PSU is no longer capable of converting the mains power into the low voltages required by PC components. The transformer required for the job would be too large and consequently far too heavy. Instead, we use switching power supplies that employ the same frequency trick as the good old tube radio. Their job is to provide the required voltages and currents as efficiently as possible, while also reliably maintaining those levels. Analog (linear) solutions are no longer viable solutions. Instead, we now rely on transistors as switches to convert the mains power into higher frequencies, allowing us to use smaller transformers to transmit high power levels. Indeed, this is where the term “switching power supply” comes from. We’ll cover how those work in more detail in the next chapter. Don’t worry, it’s all simpler than you might think.

2. How A Switching Power Supply Works

What's Inside, And How Does It Work?

A switching power supply consists of several stages. A filter for the mains power sits right behind the input, filtering out surges, harmonics, and various other undesirable phenomena found in the mains power. In the second stage, the AC current is rectified and screened. At this point, we’re dealing with about 350 V, which are then transformed through an inverter stage, yielding an alternating current with a frequency between 35 and 50 kHz. This is where our small transformers come in, converting the alternating current.

Eventually, differing voltages of 3.3, 5, and 12 V are required, which means that simple PC switching power supplies have either a single output rail with different taps for each voltage or separate rails for each voltage. Top-end PSUs even have separate transformers for different voltages, which are then corrected and smoothed a second time following transformation. The most important thing is that these voltages have to stay consistent. Regardless of whether the PC is idling or under full load, voltages may not deviate from their spec by more than 5 percent.A regulator circuit ensures this is the case. This is also the reason a switching power supply is always connected to a load. Otherwise, you risk a voltage flashover.

That brings us to our next topic: efficiency. If you’re looking for a new car, you’re going to ask your local dealer, “So, how many miles per gallon does this one get?” Now, PSUs may not burn gasoline, but you still have to look out for their efficiency. Indeed, this is one area where most builders unknowingly waste the most power, increasing the PC's cost over its lifetime. Want to make sure you don’t make that mistake? Take a look at the next page!

3. Efficiency, Efficiency, Efficiency!

“How Much Do I Get Out, When I Put This Much In?”

While this is a valid question, we should probably rephrase it a little. Usually, you call the ratio between the amount of power drawn (from the wall wart) and the amount of power that is put out (to the computer) efficiency. The lower the amount of power a PSU has to draw in order to output a specific target power, the higher its efficiency.

While we’re at it, we’d like to clear up a very common misunderstanding regarding efficiency. If you have a 500 W power supply with an efficiency of 75 percent, that doesn’t mean it can only output 375 W to the PC. Instead, it has to draw 666 W from the wall in order to provide 500 W to the computer. So, the correct version of our question is, “How much power does my PC draw from the wall when it requires a certain amount of power?”

Example:

Let’s assume we’re really pushing our PC and it needs 600 W. Our PSU is rated at 80% efficiency. Here’s what it’s really drawing from the grid:

 600 W / 0.80 = 750 W

Ideally, our PC will draw about 750 W from the wall under load. The remaining 150 W are, quite simply, wasted, and usually dissipated by the PSU as heat.

Nothing Is Constant, Not Even Loss

Our example above only holds true in an ideal world though, and since we don’t have super-efficient Star Trek technology, things usually don’t end up being that straightforward. A computer is used in various states, ranging from idle to full throttle, if you will, with every shade in between. Obviously, it will use the least power while idling on the desktop, more in casual use, and most under full load (3D graphics or intense calculations). Thus, we can’t expect to see constant power usage. Instead, we have to assume at least two states, namely idle and load. Now, let’s take a look at the efficiency of our hypothetical 600 W power supply under various loads.

Uh-oh; what’s this? Our nice, straightforward explanation seems to get bent out of shape in that graph. Looking at the curve, we can see that the PSU reaches its peak efficiency at about 50% of its nominal capacity.

Now, a clever observer would suggest that simply making the PSU twice as powerful should solve that problem. While this is correct in principle, that same clever observer would be forgetting something: the idle state. And this is where modern switching power supplies run into trouble. If their load drops to below 20%, their efficiency plummets to 60 or 50%, possibly even less. Ironically, this situation is only exacerbated by the power-saving mechanisms implemented in modern PC components. For example, a powerful system with a good graphics card can get by with as little as 65 W when idling, but draw a good 500 W under load. Thus, you have to ensure that the PSU is neither overtaxed nor under-challenged.

Example:

This time, let’s say our 600 W PSU is supplying 65 W to the system. What load does that correspond to?

(100% / 600 W) * 65 W = 10.83%

Now, take a look at our chart, and you’ll see things aren’t looking too good. Houston, we have a problem. Let’s repeat our calculation, this time assuming a 68% efficiency, as suggested by the chart.

65 W / 0.68 = 95.6 W

Despite the fact that the system really only requires 65 W, the PSU is drawing almost 100 W from the wall and turning the remaining 30 W into heat. And these are the numbers for the more efficient of the two hypothetical power supplies, too! Not to get ahead of ourselves, but there were two efficiency curves in that diagram, one for a cheap power supply and another for a more expensive one. And wouldn’t you know it, the supposedly cheap (and fictitious) DragonMegaHyperCombatUltra PSU for 30 bucks turns out to be a real power hog when the system is idling, driving up your power bill in the long run.

Again, this is only a hypothetical example. For our next trick, we’d like to show you what actually happens. As it turns out, we can easily allow for the impact of efficiency in our calculations. Oh, and it’s just as easy to prove that cheap PSUs will often turn out to be a lot more expensive than you might think in the long run.

4. Of Power Factors, Apparent Power, And Effective Power

PFC (Power Factor Correction): It Does What It Says

Don’t worry, you won’t need your high school physics text book for this part. We just want to point out another characteristic that can be used to tell a high-quality PSU from a bad one. Once you know the basics, you’re a lot less likely to make a bad purchasing decision. So, let’s dive right in.

Idle Current And Idle Power

One problem that plays an especially big role in the case of switching power supplies is the so-called idle current which results from inductivity. Note that idle current has nothing to do with the idle state of your computer. This idle current only transports energy between a generator and a load, but doesn’t end up benefiting the load in any way. Again, load in this context has nothing to do with a PC at full throttle, but refers to a component that uses power. Think of it as a power shuttle that isn’t involved beyond its role as a transporter. This idle current has to be reduced as much as possible and as early as possible, since it causes power loss in conjunction with ohmic resistors, manifesting itself as heat. This idle power consumption is a waste, and should be kept as low as possible through appropriate circuitry.

Effective Power And Apparent Power

Unlike idle power consumption, effective power measures the power that is actually used, while apparent power refers the sum total of the effective power and the cumulative idle power.

Power Factor

This factor is the result of the ratio between effective power and apparent power, falling somewhere between 0 (worst) and 1 (ideal). Thus, you should always ensure you are buying a power supply with a high power factor, since the factor is an extremely good indicator of the quality of the PSU circuitry.

Practical Application

Active PFC

As the name implies, active power factor correction (PFC) employs a circuit that actively corrects the power factor. As we just explained, the power factor is an important parameter in the world of PSUs, since it describes the ratio between effective power and apparent power:

Pros:
• An almost ideal effective power of nearly 99%
• Very stable current output
• Very low power loss
• Very low heat dissipation
• Does without iron, leading to reduced weight

Cons:
• Higher initial cost
• More susceptible to faults
Passive PFC

Passive PFC attempts to reduce idle currents by using large choke coils. While this method is simpler and cheaper, it is also much less effective.

Pros:
• Cheaper
• Practically no electro-magnetic interference


Cons:
• Requires better cooling
• Not suitable for higher power levels
• Increased power consumption due to power loss
• Heavier due to the choke coil
• Lower effective power ranging from 70% to 80%

Power supplies with passive PFC should be considered outdated and can be considered inferior.

Note: Do not confuse efficiency and PFC!
5. How To Spot An Efficient PSU?

Guidelines, Rules, And Regulations

One of the most important indicators of a PSU’s efficiency is whether it complies with the Energy Star 5.0 guidelines and the 80 PLUS standard. The latter applies primarily to computer power supplies and is recognized worldwide. Additionally, if you’re located in a European country, CE conformity and compliance with ErP guidelines are also important.

80 PLUS PSUs Are More Efficient

The specifications, norms, and guidelines we just mentioned all call for high efficiency, as well as improved power quality. Power supplies that conform to these demanding and very strictly-interpreted rules by passing a defined set of tests may then be marked with the 80 PLUS badge appropriate to its efficiency level. While the load/stress tests may not correspond to those defined by the ATX specification, that’s acceptable in this case. Here’s some good news for our European readers: since the tests are conducted using the lower US voltages, these power supplies achieve even higher efficiency levels in the European 220 V grid.

80 PLUS: Platinum, Gold, Silver, Bronze

The original concept of the 80 PLUS certification has been revised, adding new, more strictly-defined efficiency levels. The bronze, silver, gold, and platinum certifications each come with their own requirements. Thus, a PSU that is certified “80 PLUS Gold” or “80 PLUS Platinum” is more efficient than a normal unit. The downside is that the more complex circuitry needed to hit those levels generally results in a higher price tag, too.

Below you’ll find a table that shows what efficiency levels a PSU has to achieve at a given load to make the grade for a specific certification level.

 Efficiency at 20% Load
Efficiency at 50% LoadEfficiency at 100% Load
80 PLUS80%80%
80%
80 PLUS Bronze82%85% 82%
80 PLUS Silver85%88%85%
80 PLUS Gold87%
90%87%
80 PLUS Platinum90%92%89%


When Off Isn't Really Off: A Few Words On Standby Power Consumption

When you shut down your computer, the PSU doesn’t really switch off completely. This is necessary for features such as Wake-on-LAN to work. The point is that the power supply keeps drawing some power, even when the computer is off. Newer PSUs, especially ones sold in Europe and certified to be ErP/EuP-compliant, draw less than 1 W in this standby mode. If you’re serious about conserving power, go for a newer model with ErP support.

Which Power Rails Are Important?

That brings us to one of the most crucial points of modern power supplies: namely, the power they are able to supply at various voltages. Nowadays, PCs draw the majority of their power from the +12 V rail. By comparison, the other two voltages, 3.3 and 5 V, play a far less important role. That’s why you can use the following as a rule of thumb: if a PSU’s 12 V rail can supply all of the required power with room to spare, then the lower voltages are sufficient as well.

However, the opposite is not necessarily the case. Let’s compare the spec stickers of two PSU models:

The difference is quite obvious. Although the second model is billed as a 550 W unit, its +12 V rails only add up to 380 W, and even that only holds true if the other rails aren’t being stressed simultaneously! Nobody needs 315 W on the 3.3 and 5 V rails. In practice, this power supply would probably reach its limit at a load of 350 W on the 12 V rail.

Ironically, even a good 425 W PSU could push more power than this model at 12 V. Don’t fall for this sort of trickery. 

Initial Cost Vs. Energy Savings

Quality products cost more initially, but that doesn’t necessarily always translate into lower cost in the long run. That’s why we’ll take a look at a few specific components and their prices in a moment to determine the type of PSU makes the most sense in a given environment, and what kind of savings you can achieve, if any. Some of the results may surprise you!

It’s not enough to focus solely on the financial aspect, though, because we also have to consider durability, reliability, and safety. We go into more detail on these points on the next page.

6. Don't Get Burned: Safety Before Stinginess

Chinese Firecrackers

While this description may sound a little whimsical, there’s a serious implication to consider. Often, what seems like a bargain can turn out to be a potentially flammable firecracker that can take out your whole system when it makes its grand exit.

The Most Important Protective Circuits In Modern PSUs

Knowing is half the battle, so says the G.I. Joe PSA, and that’s why we want to present this info. Below you’ll find a table with the most important abbreviations for protective mechanisms found in modern power supplies. If you make sure these features are included with your PSU of choice, you can prevent your hardware from falling prey to an unnecessary failure.

Abbreviation Protection
OVP
Over-Voltage Protection (primary and secondary)
UVP Under-Voltage Protection (primary and secondary)
NLO No-Load Operation
SCP
Short-Circuit Protection
OCP Over-Current Protection
OLP (OPP) Overload Protection
  OTP Overheating Protection



A decent PSU should contain a digital protection chip. Sadly, there are still some companies that sell super-cheap models with a conventional fuse and varistor as “equipped with short-circuit protection and over-temperature protection.” While this may be true by the letter of the law, a combination like that is a recipe for disaster.


When Buying Cheap Can Be Really Expensive


Here we have two perfect examples of what can happen when a company cuts corners; things can get really hot. We think these pictures speak for themselves. Do yourself a favor and get a decent power supply.

And with these educational images, we’ve come to the end of our primer on switching power supplies. Now that we’ve gone over the theory, it’s time to apply what we learned to the real world. To that end, let’s look at some of the components in a computer and how much power they consume.

7. How To Determine Your Power Requirements

A Matter Of Simple Addition

While there are many online calculators out there meant to help you figure out how much power your build will use, they all share one major weakness: they are all based on the build’s maximum power requirements. They then take into account the PSU’s maximum efficiency at a load of 50 to 55 percent and make a (generous) projection based on those numbers. The drawback is that this method does not consider power consumption when the computer is idle. As we pointed out on page three, that’s where things tend to get really ugly, efficiency-wise.

The following table is meant as a guideline, showing you how much a certain component is likely to use under a specific load. If you know the exact figures for your components, you can just plug them in instead and do the math.

 Component Type
    Description Idle (W)Load (W)Number Installed
CPUCurrent dual-core CPU
Current dual-core CPU, overclocked
Current quad-core CPU (Mid-range)
Current quad-core CPU (High-end)
Current quad-core CPU, overclocked (High-end)
Older dual-core CPU (AMD)
Older dual-core CPU (Intel)
Older single-core CPU
20
25
35
40
45
35
55
35
65
90
95
125
140
90-125
125-140
60-90
1
MotherboardCurrent microATX board without graphics
Current microATX board with graphics
Normal mid-range board without graphics
Normal mid-range board with graphics
High-end board
High-end board, overclocked
15
30
20
25
35
40
25
40
35
50
45
55
1
RAMCurrent DDR2 or DDR3 RAM, per 2 GB module
Current DDR2 or DDR3 RAM, per 4 GB module
Overclocked RAM per module (estimated)
2
3
4
4
5
6
1 - 4
HDDConventional hard drive28 - 10Varies
SSDCurrent solid-state drives14Varies
ODDDVD-ROM only
DVD burner
Blu-ray reader/burner
1
1
2
6
10
12
1
FanNormal CPU fan, mandatory
Silent case fan
Performance case fan
1
2
3
1 - 3
2
3
1
Varies
Varies
Add-In CardExternal sound card
TV card
Controller card
2
1
1
8
2 - 5
2
0 - 1
0 - 1
Varies
Graphics Cards
Current office-oriented card
Current mid-range gaming card
Current high-end gaming card
10 - 16
16 - 30
25 - 35
35 - 75
75 - 180
180 - 375
1
1 - 2
1 - 2
OtherCold cathode lighting, modding parts, etc.See manufacturer infoVaries


Now that we have an idea of how much power each of these components draws, calculating the overall power consumption when idling and under load is simple. Based on this information, we will define a power window in the next chapter and choose the best PSU for the job based on their individual characteristics.

8. The Power Window Is Important

Pegging Idle And Load Power Usage

Let us examine the characteristics of three typical usage scenarios. Now, we know that many mechanisms and techniques can help to reduce power consumption when the system has nothing to do. This is especially true for very powerful systems. That also means that the range of power levels at which they operate increases as well. In other words, they are quite frugal at idle and very demanding under full load. This so-called power window allows us to better define a system's individual requirements.

To illustrate the next part of the analysis, we are using four PSUs as examples. These include a cheap, high-powered model from the bargain bin (the purple line), an 80 PLUS-certified PSU (blue), another 80 PLUS Bronze model (orange-brown), and finally an 80 PLUS Gold option (yellow), capable of delivering between 500 and 525 W.

In the case of our super-cheap power supply, we decided to use a 750 W model to ensure that it’d be able to actually reach 500 W. Now when we take a look at their respective efficiency curves in a given scenario, we can see some pretty obvious (and unpleasant) differences:

As we can see, simply buying an efficient 500 W power supply is not a one-stop solution. To the contrary, these graphs should help us appreciate that choosing the right “size” power supply is at least as important as its quality and efficiency. You can only achieve an optimal result when all three factors are taken into consideration.

9. Example 1: The Office PC

Test Case 1: Office PC

Here’s a look at our standard office PC.

Office PC
CPU
Intel Core 2 Duo E8400

Motherboard
Abit I-N73H
RAM
2 x 2 GB DDR2 Kingston Value RAM
Graphics
On-board
Hard Drive
1 x 500 GB Western Digital Caviar Blue
Optical Drive
DVD burner
External Devices
Mouse, Keyboard
Power Draw, Idle
53 W
Power Draw, Normal Load
90 W
Power Draw, Full Load
122 W
Power Meter
Energy Logger 4000 (Conrad Electronic)

• Long-term measurements
• Monitoring
• Consumption measured up to 1.2 kW


Our goal is to find a suitable power supply for this job. We’ll have to ask our readers for forgiveness here, as this article originated with our German team from Stuttgart. While some of the power supplies used by our colleagues may not be available in the US, they still serve to illustrate the point quite well.

Also, we were hoping to use Huntkey’s Jumper 300 W 80 PLUS Gold as our standard. Sadly, the review sample we were promised got stuck somewhere between China and German customs and didn’t make it to the lab in time for this piece. That’s why the Super Flower 450 W Golden Green is taking its place today, despite being a bit on the beefy side for the job. So without further ado, here are our candidates:

ManufacturerModel
Certification
Price
Hardwaremania24
Standard ATX 420 W
none
$14 (€9.90)
LC-POWERLC6350 Super Silent 350 W
none
$28 (€19.90)
Be QuietPure PowerL7 300 W80 PLUS
$45 (€32.00)
RasurboReal & Power RAP 350 W 80 PLUS
$49 (€35.00)
Super Flower
Golden Green 450 W
80 PLUS Gold
$83 (€59.00)


Big Charts For Our Smallest System

Now for the big reveal. How do our various contenders stack up? Well, have a look for yourself. There are certainly some pronounced differences:

Nineteen watts separate the best and the worst power supply at idle, with Be Quiet and Rasurbo taking the top spots. The Gold-certified Super Flower model comes in third, with the two cheapest PSUs bringing up the rear.

That ranking doesn’t change much when we look at a normal usage scenario, where the difference between the first and last place shrinks to 11 W. However, Rasurbo and Be Quiet trade places, while the rest of the field stays unchanged.

Under load, the delta between our top performer and the worst offender increases to 14 W, with the Super Flower unit taking the lead ahead of Rasurbo and Be Quiet. Meanwhile, it seems that the efficiency curve of the super-cheap Hardwaremania24 PSU starts to fall off again, exposing this model as a rebadged 250 W model. If you want to try for 300 W with a PSU like that, keep a fire extinguisher handy.

Conclusion

In all three scenarios, the 80 PLUS-certified models take the top three spots. Interestingly, the Gold-certified Super Flower only comes out on top under full load. In this case, it doesn’t seem as though its higher price is really worth it. To be fair, it is penalized to some extent by being the highest-capacity model in this group. Super Flower does have one advantage, though, since its model is semi-passive. Under these loads, the fans don't spin up at all, making the Golden Green 450 W an interesting choice for a silent build.

10. Example 2: Mid-Range Gaming PC

Test Case 2: The Mid-Range PC

Again, let’s begin by taking a look at our mid-range build.

Mid-Range PC
CPU
AMD Athlon X4 640

Motherboard
MSI 870A-G45
RAM
4 x 2 GB DDR3 Kingston HyperX
Graphics
HIS Radeon HD 6870
Hard Drive
1 x 1 TB Western Digital Caviar Blue
Optical Drive
DVD burner
External Devices
USB hard drive, mouse, keyboard
Power Draw, Idle
78 W
Power Draw, Normal Load
126 W
Power Draw, Full Load
332 W


Next, we pick out some likely power supplies. Our choices are:

Manufacturer
Model
Certification
Price
Hardwaremania24
Standard ATX 420 W
none
$14 (€9.90)
LC-POWERLC6350 Super Silent 350 W
none
$28 (€19.90)
RasurboReal & Power RAP 350 W 80 PLUS
$49 (€35.00)
Super Flower
Golden Green 450 W
80 PLUS Gold
$83 (€59.00)
Enermax
Modu 82+ II ErP 425 W
80 PLUS Bronze
$113 (€80.00)


Two PSUs Are Killed In Action

That brings us back to our charts. Sadly, two of our contenders didn’t survive this scenario. Then again, this was hardly a surprise. Remember what we said about the spec sticker on the one unit that claimed a lot more power than it could realistically supply? Yep, that was one of our casualties. More interesting than the fact that it died at all was the point at which it happened. See for yourself:

Conclusion

Rasurbo is able to retain its lead when the system is idle. But once the computer sees a normal usage pattern, Super Flower winds up ahead, albeit by a slim margin. Despite its much higher price, the Enermax unit places third so far. LC-Power and the cheap Hardwaremania24 PSU come in last.

Under full load, Enermax can finally advance to second place, coming in right behind Super Flower. Rasurbo’s Real & Power RAP 350 W is right up against its limit, which is borne out by the decreased efficiency. It really is just a bit underpowered for this build, which is why wouldn’t recommend this combination for extended use. Downgrading to a Radeon HD 6850 would probably alleviate that concern, though.

In order to let our two low-cost candidates compete here as well, we had to use some PCIe adapters so we could power the graphics card. LC Power’s so-called 350 W model died a sudden (albeit quiet) death, giving off a hiss and a picturesque little cloud. We decided not to continue testing the Hardwaremania24 model under load, since it began giving off a pungent odor when we started up Google Earth in our “normal load” scenario. We considered that warning enough and chose to protect the remaining hardware from imminent meltdown. We’re not exaggerating that danger, either. That particular model lacks any kind of protection mechanism beyond a very sluggish micro-fuse.

11. Example 3: The Enthusiast’s System

Test Case 3: The Enthusiast’s PC

And now for our high-end configuration

High-End PC
CPU
Intel Core i5-2500K @ 4.5 GHz

Motherboard
Gigabyte P67A-UD5
RAM
2 x 4 GB DDR3 Kingston HyperX
Graphics
Gainward GeForce GTX 580
Hard Drive
1 x 1 TB Western Digital Caviar Blue
Optical Drive
DVD burner
External Devices
USB hard drives, mouse, keyboard
Power Draw, Idle
72 W
Power Draw, Normal Load148 W
Power Draw, Full Load
488 W


This time around, we choose from the following candidates:

ManufacturerModel
Certificate
Price
Super Flower Golden Green 450 W80 PLUS Gold$83 (€59.00)
RaptoxxRT 600 SPLNone
$88 (€62.00)
Aerocool VT12XT 600 W80 PLUS Bronze$115 (€82.00)
EnermaxModu 82+ II ErP 525 W 80 PLUS Bronze$145 (€102.00)
Corsair AX 75080 PLUS Gold$198 (€140.00)


A Big System Draws Big Power

We fire up our watt meter one last time, and this time, all of our PSUs survived. We purposely chose a wide spread of models for this scenario, both where price and power are concerned. Here are the results of this mixed batch of power supplies:

Conclusion

Again, we purposely pushed some of our candidates to their limit, and even beyond. The Super Flower model, nominally rated at 450 W, remained surprisingly stable throughout. Indeed, it acted more like a solid 500 W model, albeit one close to its limit.

With the system idling, the brawny Corsair AX 750 is at a bit of a disadvantage compared to the other contenders. However, as the system’s power consumption rises, so does this model’s efficiency. The Enermax Modu 82+ II ErP 525 W has no real strengths or weaknesses and ends up in the middle of the pack. It is pleasantly quiet, though. The same holds true for Corsair, by the way, which combines low noise with the highest power reserves in this group. It’s definitely not cheap, but it’s a very good entry.

Raptoxx, on the other hand, is cheap and does decently enough, if you can stand its noise level. While the extra 15 to 20 W it tends to consume compared to its competitors add up over time, none of the more expensive models would amortize their higher price through power savings. Aerocool’s VT12XT 600 W is pricier than Raptoxx‘ entry, but also quieter and a little more frugal when it comes to power use. Once more, you are unlikely to be able to recoup the higher price compared to the Raptoxx due to its lower power consumption.

12. If You Don't Like Our Advice, Buy A Fire Extinguisher

So, What Did We Learn Today?

At the end of this little analysis, we can summarize our findings in five concise bullet points.

  1. Choosing the right capacity is often more effective than choosing the wrong PSU with a higher efficiency rating.
  2. Buying too big just to be on the safe side is counter-productive and only makes sense if you actually need the reserves.
  3. Affordable 80 PLUS Gold and Bronze power supplies make sense in systems with a large power window.
  4. Don’t blindly believe the wattage numbers on the box. Be smart, think logically, check the numbers and do the math yourself.
  5. Stay away from offers that are too good to be true. You can’t get a good 500 W power supply for 40 bucks. That “bargain” might just blow up in your face. Literally.

Don't Say We Didn't Warn You!

Consider this image a warning that’s only partly tongue-in-cheek. We hope our analysis has helped clear up some common misconceptions and maybe even given you a new perspective on the mundane world of power supplies. It may be a component that gets less attention than CPUs and graphics cards. After all, it's a loss less visible, and its performance characteristics are not as impressive. But that doesn’t mean it’s unimportant, and cutting corners to save money may end up costing you a lot more in the long run.