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Part 2: Four Cheap 80 PLUS Bronze Power Supplies, Reviewed
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1. At $45 And Up, We Reach For Power Supply Gold

Part one of our budget power supply round-up debated the merits of four PSUs ranging from 350 to 550 W, all of them flashing 80 PLUS Bronze ratings. Aside from the Cougar A350, all of them proved capable of satisfying the specification. Today we're looking at four more power supplies, this time ranging from 360 to 550 W. The range is a little narrower, but the contenders are all still quite comparable. Three sport the same Bronze logo, but one, Seasonic's SSR-360GP, boldly claims compliance with 80 PLUS' Gold standard, typically reserved for $100-plus products. All the while, the SSR-360GP sells for a mere $60.

Although that aggressive price gets our attention, we aren't going to neglect the other three test candidates: Cooler Master's Silent Pro M2 520W, Corsair's CX500, and Gigabyte's Greenmax Plus 450W. That Gigabyte unit doesn't seem to be available in the U.S., but with 550 W and 650 W versions showing up on Newegg, we're hoping to see the 450 W model soon.

As with yesterday's story, we again asses the sound levels of each PSU. This is something readers have been requesting for a while. Until now, though, we lacked a practical and reproducible methodology. From now on, we'll be measuring acoustics at three load levels: 40 W, which simulates an idle PC or a machine running office applications; 200 W, standing in for a mid-range gaming workload; and a 600 W draw to replicate what a more extreme gaming PC might encounter with a couple of graphics cards installed. That should get each unit's cooling fan spinning as fast as possible. Of course, if 600 W exceeds the maximum output of a power supply, we made do without it and simply use the other two.

In order to simulate these loads, we built a test fixture consisting of 12 V/40 W light bulbs, which imposes a purely resistive load on the power supply. With 15 lights, we can simulate any load between 40 W and 600 W, in 40 W steps. We are aware of the fact that a purely resistive load may stress a power supply differently than the partly capacitive, partly inductive load of a real-world PC. But we’re not overly worried; this synthetic load should be perfectly suited for measuring the sound level of the PSUs at each load level. Acoustics are measured one foot away from each power supply's fan, and we let each unit settle for half an hour any time we change the load.

Note that, in part one, we talked about a unique anomaly exhibited by one of our instruments. In short, after we upgraded oscilloscope probes to better ones, all of the PSUs we tested started showing spikes that the previous, less expensive probes never displayed. After some back-and-forth with a couple of power supply vendors, we came to the conclusion that our new probes allow us to pick up short spikes that the old ones missed.

2. Cooler Master Silent Pro M2 520W

Cooler Master is fairly general in targeting its second-generation Silent Pro M series at pretty much any PC. This 520 W power supply is about the right size to handle anything from office computers to mainstream gaming machines, though. The Silent Pro M2 520W is the only power supply in our round-up that sports modular cable management. Every lead except the 24-pin ATX and ATX12V cable is flat, something Cooler Master is now known for.

Cable quality is excellent, and so is our overall impression of this PSU. Each lead is sufficiently long; we'd even go so far as to say generously so. Thanks to a pair of 6+2-pin auxiliary PCI Express connectors, you can natively support CrossFire or SLI without adapters, so long as you're using cards with one input. While the large number of peripheral connectors (six SATA and four Molex) is impressive for this round-up of budget PSUs, it may impact the price. As it is customary for Cooler Master PSUs, the Silent Pro M2 PSU sports a single-rail design, and its 12 V rail can supply up to 40 A.

Cooler Master Silent Pro M2 520W
AC Input100-240 V, 50-60 Hz
DC Output+3.3 V+5 V+12 V (#1)+12 V (#2)+12 V (#3)+12 V (#4)-12 V+5 Vsb
20 A22 A40 An/an/an/a0.3 A2.5 A
Individual Output     3.6 W12.5 W
Rail UtilizationSysSysCPU & VGA
Combined Output120 W480 W
Total Continuous Output520 W
Peak Output580 W

3. Cooler Master Silent Pro M2 520W: Measurements

Efficiency According to the 80 PLUS Spec

Efficiency by Load

Like all of the power supplies in yesterday's and today's stories, Cooler Master's Silent Pro M2 exhibits short spikes on the supply rails. Only the new higher-quality oscilloscope probes are able to pick them up. On the 12 and 3.3 V rails, these spikes exceed the maximums specified by the ATX spec. However, since every sample demonstrate the same phenomenon, we're not counting this against any of them.

When the brief spikes are not taken into account, this 520 W power supply easily complies with the ATX spec. It's also 80 PLUS Bronze-compliant. At 50% and 100% load, it even offers significant efficiency reserves. While standby power draw and inrush current are average, the Silent Pro M2's hold-up time is best-in-class at 27 ms. We have no complaints about the sound level of the Cooler Master PSU, either. It lands around 31 dB(A), regardless of whether we apply 40 W or 200 W of load.

A Close Look at the PCB

The 135 mm fan inside Cooler Master's Silent Pro M2 is made by Young Lin Tech, model DFS132512M and sports a liquid bearing. The large cooling fins almost have a retro look, since most modern PSUs have smaller fins, enabled by better efficiency and less heat output. The input filter has all necessary components, in this case two X capacitors, two Y capacitors, two choke coils, and a MOV. While the large capacitors are made in Japan by Matsushita and Panasonic, the smaller ones are manufactured by Taiwan-based Teapo. We liked the soldering quality.

4. Corsair CX500

Like the Seasonic SSR-360GP, Corsair's CX500 sells for about $60 online, which we think is a really good price for a 500 W PSU. Was this achieved by going cheap? Judging from the excellent workmanship and Corsair's technical specifications, we don’t think so. The non-removable cables are all fully sleeved. You get two 6+2-pin auxiliary PCI Express connectors and plenty of well-spaced peripheral leads as well. The cables are sufficiently long, too.

A partially modular version of this same power supply is called the CX500M, and it costs about $18 more (we found it for $78 online).

Corsair CX500
AC Input100-240 V, 47-63 Hz
DC Output+3.3 V+5 V+12 V (#1)+12 V (#2)+12 V (#3)+12 V (#4)-12 V+5 Vsb
25 A20 A38 An/an/an/a0.8 A3.0 A
Individual Output      9.6 W15 W
Rail UtilizationSysSysCPU & VGA
Combined Output120 W456 W
Total Continuous Output500 W
Peak Output550 W

5. Corsair CX500: Measurements

Efficiency According to the 80 PLUS Spec

Efficiency by Load

Corsair’s budget-oriented PSU passes our lab tests with nary a hitch. When we check the efficiency, we find that the CX500 not only complies with 80 PLUS' Bronze spec, but has some leeway at medium and full load. Even operating at a low load, it is quite efficient (80% at 50 W, for instance). Measuring ripple and noise, the PSU not only complies with the ATX spec, but surprises us by keeping those brief spikes inside the specification as well on its 12 and 3.3 V rails.

When we disregard the spikes, the ripple and noise values are excellent. Standby power draw and inrush current are among the lowest in our field of contenders. But when we measure hold-up time, which protects against brief brownouts, we saw a result shorter than 16 ms, which is the ATX specification's floor (we saw 14 ms at both 115 and 230 V). At 31.5 dB(A), this PSU is insignificantly louder than Cooler Master's Silent Pro M2.

A Close Look at the PCB

When we spot the green transformers, we immediately know that Corsair's CX500 is manufactured by Channel Well Technology. The interior layout is very clean and the soldering quality is excellent. The large capacitor on the primary side is manufactured by Samxon, which is part of the China-based Man Yue Technology holding. On the secondary side, there are also some Samxon capacitors, but also some capacitors manufactured by Teapo in Taiwan. In spite of its low price, no important components fall victim to cost cutting. For instance, the input filter sports two X capacitors and four Y ones, two coils, and a MOV.

6. Gigabyte Greenmax Plus 450W

Gigabyte, mostly known for its motherboards and graphics cards, is participating in one of our power supply round-ups for the first time. Its Greenmax Plus 450W is a good fit for this budget-oriented comparison. Currently, only the company's 550 and 650 W Greenmax models are available in the U.S., but based on their pricing, we expect the 450 W version to show up in the $50 to $60 range.

Since this is not a high-end PSU, we aren't surprised by its fairly standard features. Its build quality seems OK, but not outstanding. The cables are non-modular and fully sleeved though, which is nice. The cable lengths and the number of connectors are average. There are but three Molex connectors and only one 6+2-pin auxiliary PCI Express connector. So, this power supply isn't really suitable for dual graphics cards, or even a gaming rig with one high-performance card (though that should have been pretty obvious in light of its maximum output). The 450 W PSU sports two +12 V output rails, each of which can deliver up to 25 A for a combined maximum of 32 A. No screws or Velcro bands are included.

Gigabyte Greenmax Plus 450W
AC Input100-240 V, 50-60 Hz
DC Output+3.3 V+5 V+12 V (#1)+12 V (#2)+12 V (#3)+12 V (#4)-12 V+5 Vsb
20 A21 A25 A25 An/an/a0.5 A3.0 A
Individual Output  32 A  6 W15 W
Rail UtilizationSysSysCPU & VGA
Combined Output120 W378 W
Total Continuous Output450 W
Peak Output550 W

7. Gigabyte Greenmax Plus 450W: Measurements

Efficiency According to the 80 PLUS Spec

Efficiency by Load

Of course, lab results matter more than bundled goodies. So, let’s start with our two pet peeves: ripple and noise. Like all of the power supplies in our round-up, we observe brief spikes on the output rails. They're most pronounced on the 5 and 3.3 V rails. While even the 12 V rails exhibit spikes, they are within the ATX specification's limits. When we disregard the peaks, the oscilloscope's waveforms look a lot nicer.

The Greenmax Plus 450W's efficiency is almost on a par with Cooler Master and Corsair, which is to say it's good. This 450 W power supply stands out from the crowd in two ways. First, its inrush current is quite high at 230 V (62 A). On the other hand, its hold-up time is approximately 25 ms, or almost twice as good as the Silent Pro M2's hold-up time. However, the Greenmax Plus is outclassed by other PSUs when it comes to our acoustic measurements. We observed up to 35.5 dB(A), which is quite audible in a quiet room.

A Close Look at the PCB

The Greenmax Plus 450W's yellow PCB is somewhat smaller than the chassis can fit, which means the layout is necessarily compact. The cooling fins are pretty diminutive compared to Cooler Master's, for example. But we noticed that Gigabyte still uses quality components; there's no cost-cutting we can readily identify. The main capacitor on the primary side is made by Japan-based Nippon Chemi-Con, while the other capacitors are made by Samxon (we already encountered this brand inside Corsair's CX500). While the input filter is not split into two parts, we found all necessary components. We also found the soldering quality to be OK.

8. Seasonic SSR-360GP

We were excited when we received the Seasonic SSR-360GP, an 80 PLUS Gold-certified power supply selling for $60. The manufacturer seems to be suggesting that efficiency is becoming more important than raw output potential. It should come as no surprise, then, that this PSU offers the lowest power ceiling in today's field, maxing out at 360 W. There are plenty of applications for a low-power, high-efficiency power supply though, so does this one live up to its claims?

While the case quality does not measure up to higher-end Seasonic models, such as the X series, it's still acceptable. The same goes for this unit's fully sleeved, non-modular cables. Unfortunately, the cable lengths leave something to be desired. They're comparable to what Gigabyte gives you, except that you get fewer connectors. On the bright side, if you want to use two floppy drives, this power supply supports such a configuration (yes, we're being sarcastic).

It's a nice touch to see Seasonic bundle four screws, a few cable ties, and Velcro bands with its SSR-360GP. None of today's other contenders do this. Those items cost pennies, but they're valuable to builders looking to achieve a clean installation.

Seasonic SSR-360GP
AC Input100-240 V, 50-60 Hz
DC Output+3.3 V+5 V+12 V (#1)+12 V (#2)+12 V (#3)+12 V (#4)-12 V+5 Vsb
20 A21 A25 A25 An/an/a0.5 A3.0 A
Individual Output  32 A  6 W15 W
Rail UtilizationSysSysCPU & VGA
Combined Output120 W378 W
Total Continuous Output450 W
Peak Outputn/a


9. Seasonic SSR-360GP: Measurements

Efficiency According to the 80 PLUS Spec

Efficiency by Load

Proudly displaying the 80 PLUS Gold logo on its box, Seasonic's SSR-360GP has something that no other power supply in our two-part round-up offers, and we're eager to test it. The efficiency requirements are significantly higher for a Gold-certified PSU than the Bronze-rated ones. For all three load scenarios, the efficiency minimums to qualify for 80 PLUS Gold are five percentage points higher, in fact. And Seasonic's SSR-360GP satisfies those stringent requirements without a problem. At 20% and 50% of its maximum load, the supply complies with little leeway to spare, while its efficiency at full load is noticeably better than the Gold tier's requirement. Seasonic extends its 5% advantage over the other PSUs even into low-load conditions. At 25 W, its efficiency is an admirable 75%.

The scope picture again reveals spikes that seem to plague all of the lower-end PSUs in our round-up. If we take them into account, all of Seasonic's DC rails would violate the ATX spec. But because we're looking past them, the waveforms look OK, if not a little more jagged than we'd expect. The SSR-360GP passes all other tests without a problem. It is also barely audible. We measured 30.2 dB(A) at 40 W and 30.6 dB(A) at 200 W; you'd only hear that with an ear close to the power supply.

A Close Look at the PCB

Building an 80 PLUS Gold-rated PSU to sell at $60 is quite a challenge, even for a company like Seasonic, since the high-quality parts are more expensive. Thus, money has to be saved elsewhere. For instance, we notice that the SSR-360GP's soldering quality, while OK, does not approach what you'd find on the company's flagship X-series. However, the electrical design is still quite modern, utilizing a DC-DC converter and an LLC resonance converter. Almost all capacitors are made in Japan. We found capacitors from Hitachi, Chemi-Con, and Rubycon. A few capacitors are made by Korea-based Enesol. All necessary components are there, and the component layout looks nice.

10. Test Configuration, Hold-Up Time, And Inrush Current

Test Configuration

Test Hardware
AC SourceChroma Programmable AC Source 6530
Power MeterYokogawa WT210 Digital Power Meter
Loads4 x 600 W Chroma 63306 for 12 V testing

4 x 300 W Chroma 63303 for 5 and 3.3 V testing

using Chroma HighSpeed- DC Load Mainframes 6334 
OscilloscopeTektronix DPO3034 Digital Phosphore Oscilloscope (300 MHz)
Test Procedure
Voltages110 and 230 V
Standby Power0.25 A fixed current to simulate PC standby power on 5 Vsb
80 PLUS Efficiency Testing100/50/20% load, relative to specified total output
Load distribution across 12/5/3.3 V rails at the same proportion as specified for 100% testing at 110 V according to ATX 2.3 specification
Efficiency at Fixed Loads25, 50, 85, 300, 500 W loads
Load distribution across 12/5/3.3 V rails at the same proportion as specified for 100%
Peak Load Test110% Overload Testing at maximum combined 12 V
Temperature TestAir intake vs. Outtake temperature delta
tracking highest delta during all tests

More test results for this PSU and others can be found in our Power Supply Charts.

Hold-Up Time and Inrush Current

11. Efficiency According To The 80 PLUS Spec, Standby Power, And Sound Level

More test results for this PSU and others can be found in our Power Supply Charts.

Efficiency According to the 80 PLUS Spec

Standby Power


Sound Level

12. Part 2: Which One Of These PSUs Is Right For You?

In yesterday's half of this round-up, we suggested that it is possible to find a well-built, efficient power supply at a value-oriented price. But don't be duped by cheap PSUs. An 80 PLUS Bronze logo is not a promise of quality. In fact, Cougar's A350 is advertised with the Bronze rating and can't even achieve the necessary efficiency levels to justify that badge. Fortunately, all of the power supplies in part two at least satisfied the efficiency specifications they advertise. Nevertheless, our testing still uncovers a handful of weaknesses spread through the field.

We'll start with a power supply that appears free of any serious issues: Cooler Master's Silent Pro M2 520. Modular cable management helps it stand apart from the crowd, and its workmanship is darned near perfect. For all of that, however, you'll need to pay a price at the upper end of our budget range. The Silent Pro M2's hold-up time and sound level results are both commendable. If you want above-average power and are thinking of building a more graphics-heavy system, you should consider this PSU, though remember it's not available in the U.S. yet, so you may find yourself shopping for the 550 or 650 W versions instead.

Corsair's CX500 is rated for 20 W less, but at a retail price of $60, it is also less expensive. Apart from its lower maximum output, the CX500 loses modular cable management compared to Cooler Master's offering. And ready availability in the U.S. means we'd be more inclined to favor Corsair's offering. After all, you still get a pair of auxiliary PCI Express power connectors, along with quality that leaves almost nothing to be desired. Workmanship, interior construction, sound level, and efficiency are all good. The CX500 would be close to perfect, actually, if there wasn't an issue with its short hold-up time. All in all, this is decent budget-oriented PSU.

Too-few connectors and relatively low power output are the two biggest detractors from Gigabyte's Greenmax 450 Plus. It also doesn't help that we're not finding it for sale in the U.S., making it impossible to judge its value proposition. Should it show up soon, know that its electrical quality is impressive, aside from high inrush current. On the plus side, its hold-up time is very long. We do take issue with the power supply's acoustic output. Gigabyte's submission is the loudest of the PSUs we tested, and that applies to both load profiles. A sound level above 35 dB(A) cannot qualify as quiet. Sorry.

Maxing out at just 360 W, Seasonic's SSR-360GP seems pretty puny compared to the other power supplies in our round-up. However, it's also the only PSU bearing an 80 PLUS Gold rating for a scant $60. It delivers on that promise, too. Its outstanding efficiency runs rings around the other test candidates. Unfortunately, it doesn't give you many connectors. Great efficiency translates to less waste heat. As a result, the SSR-360GP's fan doesn't have to spin very fast. We measured just a tad over 30 dB(A), which is very quiet indeed.

13. Model Comparison Table
Overview: Efficient Budget PSUs, Part II
MakeCooler MasterCorsairGigabyteSeasonic
ModelSilent Pro M2 520WCX500Greenmax Plus 450WSSR-360GP
Price
N/A$60N/A$60
Certification80 PLUS Bronze80 PLUS Bronze80 PLUS Bronze80 PLUS Gold
Dimensions (BxTxH)5.9” x 6.4” x 3.4”5.9” x 5.5” x 3.4”5.9” x 5.5” x 3.4”5.9” x 5.5” x 3.4”
Gewicht5 lbs.
4.8 lbs.
3.7 lbs.
4 lbs.
Operating Temperature
32°-104°F
32°-122°F
104°F max.
32°-104°F
Garantie
5 Years
3 Years3 Years5 Years
Technical Specification
SpecificationATX12V v2.3ATX12V v2.3ATX12V v2.31ATX12V v2.3
Nominal Power
520 W500 W450 W360 W
Maximum Power
580 W550 W550 WN/A
AC Input100-240 V100-240 V100-240 V100-240 V
AC Voltage SelectionAuto voltageAuto voltageAuto voltageAuto voltage
DC Output +3.3 V20 A25 A21 A12 A
DC Output +5 V22 A20 A20 A16 A
DC Output +12 V (#1)40 A38 A25 A30 A
DC Output +12 V (#2)N/AN/A25 AN/A
DC Output +12 V (#3)N/AN/AN/AN/A
DC Output +12 V (#4)N/AN/AN/AN/A
DC Output -12 V0.3 A0.8 A0.5 A0.3 A
DC Power +12 V Combined480 W456 W378 W360 W
PFCactiveactiveactiveactive
Specified Hold-Up Time> 17 ms 8.4 ms>16 ms>17 ms
MTBF100,000 hours100,000 hours 100,000 hours 150,000 hours
Cooling
Main Fan
135 mm120 mm120 mm120 mm
Speed of Main Fan
Up to 1800 RPMUp to 1632 RPM1800 RPM500-1900 RPM
Aux. Fan
N/AN/AN/AN/A
Speed of Aux. Fan
N/AN/AN/AN/A
Cables and Connectors
20+4 pin Motherboard1x (22")1x (24")1x (22")1x (22")
CPU1x (24")1x (26")1x (22")1x (24")
PCI Express 6-pin/6+2-pin (Graphics)0/2x (24")0/2x (24" - 30")0/1x (18")1/0x (26")
Molex 4-pin (Peripherals)5x (20" - 31")4x (16" - 26")3x (18" - 30")3x (18" - 26")
SATA Power6x (20" - 31")5x (16" - 30")5x (18" - 30")4x (18" - 24")
4-pin Floppy1x (35")1x (35")1x (30")2x (31")
Special Features
AccessoriesScrewsScrews, Cable TiesN/AScrews, Velcro Strips, Cable Ties
Cable Management
YesYesNoNo