Be Quiet! Dark Power Pro 11 1200W PSU Review

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be quiet! says it's committed to building silent products, including the company's top PSU line, the Dark Power Pro 11. In this review, we will put the 1200 W Dark Power Pro 11 model to the test, which promises good performance and silent operation.

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Efficiency, Temperature And Noise

Efficiency

Our efficiency testing procedure is detailed here.

Using the results from the previous page, we plotted a chart showing be quiet! Dark Power P11-1200's efficiency at low loads, and loads from 10 to 110 percent of the PSU's maximum-rated capacity.

Image 1 of 4

With normal loads, be quiet!'s unit took over last place, whereas with light loads it managed to beat only Corsair's offering, and by a very small margin. Obviously, this platform cannot compete with other high-end PSUs in this area of capacity, and be quiet! should make the suitable modifications to rectify the situation and bring their flagship PSU offering up to speed.

Efficiency At Low Loads

In the following tests, we measure the efficiency of be quiet!'s Dark Power P11-1200 at loads significantly lower than 10 percent of the device's maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dialed were 20, 40, 60 and 80W. This is important for representing when a PC is idle, with power-saving features turned on.

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Test #12V5V3.3V5VSBPower(DC/AC)EfficiencyFan SpeedFan NoisePF/AC Volts
11.209A0.491A0.471A0.195A19.60W59.63%420 RPM19.0 dBA0.870
12.022V5.044V3.375V5.115V32.87W115.1V
22.451A0.990A0.977A0.389A39.73W73.09%450 RPM19.2 dBA0.932
12.019V5.041V3.372V5.105V54.36W115.1V
33.694A1.476A1.481A0.584A59.79W78.95%465 RPM20.6 dBA0.954
12.016V5.038V3.370V5.096V75.73W115.1V
44.926A1.984A1.958A0.785A79.75W82.29%510 RPM21.1 dBA0.966
12.014V5.034V3.367V5.087V96.91W115.1V

At low loads, efficiency was adequate, but most of the competition's PSUs offer higher efficiency at this load range. On the other hand, the output noise results are great since the PSU was inaudible, despite the high ambient temperatures at which we performed these tests.

5VSB Efficiency

The ATX specification states that 5VSB standby supply efficiency should be as high as possible, recommending 50 percent or higher efficiency with 100mA of load, 60 percent or higher with 250mA of load and 70 percent or higher with 1A or more of load.

We will take four measurements: one each at 100, 250 and 1000mA, and one with the full load the 5VSB rail can handle.

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Test #5VSBPower (DC/AC)EfficiencyPF/AC Volts
10.101A0.52W69.33%0.062
5.121V0.75W115.1V
20.251A1.28W75.29%0.132
5.115V1.70W107.6V
31.002A5.10W77.98%0.325
5.087V6.54W115.1V
43.002A15.05W76.13%0.453
5.014V19.77W115.1V
Image 1 of 2

The 5VSB rail wasn't as efficient as we wanted it to be. It didn't manage to surpass or even get close to the 80 percent mark, in any case.

Power Consumption In Idle And Standby

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Mode12V5V3.3V5VSBPower (AC)PF/AC Volts
Idle12.259V5.048V3.379V5.125V12.84W0.605
115.1V
Standby0.07W0.006
115.1V
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In the table above, you'll find the power consumption and voltage values of all rails (except -12V) when the PSU is idle (powered on, but without any load on its rails), and the power consumption when the PSU is in standby mode (without any load, at 5VSB).

Vampire power was very low with both 115V and 230V input. With such low power consumption at standby, this unit could easily achieve good efficiency on the 5VSB rail, especially at light loads.

Fan RPM, Delta Temperature And Output Noise

Our mixed noise testing is described in detail here.

The first chart below illustrates the cooling fan's speed (RPMs), and the delta between input and output temperature. The results were obtained at 37 C (98.6 F) to 49 C (120.2 F) ambient temperature.   

The next chart shows the cooling fan's speed (RPMs) and output noise. We measured acoustics from 1 meter away, inside a small, custom-made anechoic chamber with internals completely covered in sound-proofing material (be quiet! Noise Absorber kit). Background noise inside the anechoic chamber was below 18 dB(A) during testing, and the results were obtained with the PSU operating at 37 C (98.6 F) to 49 C (120.2 F) ambient temperature.

Image 1 of 2

The following graph illustrates the fan's output noise over the entire operating range of the PSU. The same conditions of the above graph apply to our measurements, though the ambient temperature was between 28 C (82.4 F) and 30 C (86 F).  

Up to around 650 W load and at normal ambient temperature the Dark Power unit's fan will spin at very low speeds, which results in an inaudible operation. Afterward, it increases its speed in order to offer sufficient airflow and push the hot air out of the unit's internals, and up to the 800 W - 850 W region it manages to keep its noise at very low noise levels. With 1 kW load and above, the PSU's noise is definitely noticeable.  Compared with most 1.2 kW units on the market today, however, be quiet!'s offering makes significantly less noise.

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Aris Mpitziopoulos
Aris Mpitziopoulos
Contributing Editor

Aris Mpitziopoulos is a contributing editor at Tom's Hardware, covering PSUs.

13 Comments Comment from the forums
  • Blueberries
    -12V Rail is very cool. These are really well built PSUs. I'd rather have a SeaSonic SS-1200 at this price range. I was expecting a better transient response change on the 5V rail, oh well.
    Reply
  • chalabam
    Interesting, but way too much focus on PSUs over the kW, when the system builder marathons had peak overclocked power at 750w (and mostly 500w) for years now.

    And those computers spend most of the time running at 50/100 w, where even this unit efficiency is poor.

    Good review, anyway, but I think that Tomshardware should focus on units that readers are more probable to buy. That info is more useful.
    Reply
  • chalabam
    16727117 said:
    -12V Rail is very cool. These are really well built PSUs. I'd rather have a SeaSonic SS-1200 at this price range. I was expecting a better transient response change on the 5V rail, oh well.

    Why you need 1200 W? What are you running?
    Reply
  • Blueberries
    16727128 said:
    16727117 said:
    -12V Rail is very cool. These are really well built PSUs. I'd rather have a SeaSonic SS-1200 at this price range. I was expecting a better transient response change on the 5V rail, oh well.

    Why you need 1200 W? What are you running?

    Just because it's rated for 1200W doesn't mean you're drawing 1200W from the wall. The PSU in the article is a 1200W PSU so it makes sense to compare the two.

    16727124 said:
    Interesting, but way too much focus on PSUs over the kW, when the system builder marathons had peak overclocked power at 750w (and mostly 500w) for years now.

    And those computers spend most of the time running at 50/100 w, where even this unit efficiency is poor.

    Good review, anyway, but I think that Tomshardware should focus on units that readers are more probable to buy. That info is more useful.

    Power supplies are more efficient and put off less heat when they're not near their maximum load. If your system draws 500W you don't want to use a 550W PSU, you would be straining the PSU. SLI/CrossFire builds with multiple graphic processors can achieve a power draw of over 750W on the PCI Express rails alone!

    I don't have a use for 1200W, but that wouldn't stop me from paying extra for better components, efficiency, and reduced noise.
    Reply
  • Aris_Mp
    indeed a PSU's peak efficiency is with typical loads (40-50% of its max rated capacity). However you should also take into account how long your system operates at full load. For example if your system is mostly working at idle or at low utilization then you will probably have more gain with a lower capacity PSU rather than with a high capacity one. On the other hand at high loads the stronger PSU will be closer to its sweet spot, having higher efficiency.
    Reply
  • Blueberries
    indeed a PSU's peak efficiency is with typical loads (40-50% of its max rated capacity). However you should also take into account how long your system operates at full load. For example if your system is mostly working at idle or at low utilization then you will probably have more gain with a lower capacity PSU rather than with a high capacity one. On the other hand at high loads the stronger PSU will be closer to its sweet spot, having higher efficiency.

    It is absolutely true that power supplies are usually at their best efficiency around 50% of their maximum load, but that doesn't necessarily mean a smaller PSU is better. An AX1500 can peak at ~94% 12V efficiency, which is really good, but even at 300W it's still producing 91% efficiency, and over 90% at 150W.
    Reply
  • Aris_Mp
    The AX1500i is a very special case :)
    Reply
  • Blueberries
    16732572 said:
    The AX1500i is a very special case :)

    Be that as it may it's important to look at all of the factors. Amperage, Ripple, Efficiency, Hold-up, etc. Most important of all of course is build integrity and architecture. The best PSUs do have high loads, because well, they can handle it. They'll also last longer at any load.

    An average load for an i7 user with a single high-powered video card is ~350W (gaming), a 980ti under maximum stress can be a 300-350W draw alone, bringing that up to a potential ~550W. In this scenario an RM750X is gold rated and will perform better than a Supernova P2 650W which is platinum rated. Both are extraordinary power supplies and I'd use either one. My point is, maximum load shouldn't matter. If a power supply meets more than your demands consider that a good thing. Most people aren't going to buy these PSUs unless they have a use for them because there's other options available.

    The Dark Power Pro 11 in this article retains >90% efficiency from 200W-800W, which is a wide range, and your system load would want to fall between that range to be in the "sweet spot." A smaller PSU has a much smaller "sweet spot," but it could prove to be better.
    Reply
  • mctylr
    indeed a PSU's peak efficiency is with typical loads (40-50% of its max rated capacity). However you should also take into account how long your system operates at full load.

    It is absolutely true that power supplies are usually at their best efficiency around 50% of their maximum load, but that doesn't necessarily mean a smaller PSU is better.

    All switching power supplies decrease their efficiencies as their load decreases, typically starting at or near 50% load and often rapidly decreasing efficiencies as their load falls below 20%.

    For desktop systems, unless you run a distributed computation project in the background, 80-95% of the time the system is powered on, the system is idle or near-idle. In my limited testing a desktop system likely draws 50-100W at idle, so with a 1000W power supply it's operating at 5-10% load, and thus at its worst efficiencies.

    With Haswell and newer consumer Intel's CPUs maxing out at 145W (I believe) at stock frequencies, and most video cards needing under 200-250 W maximum (980Ti 250W), a system with a single GPU rarely needs more then 600W.

    Specifying the PS for 50% load (for maximum efficiency) to match the maximum load the system is actually capable of drawing is a poor efficiency trade-off, as the system will spend the majority of time time at under 20% utilization, at its worst efficiency, that the few percentage points of increased efficiency (at 50% load versus moderately higher loads) will result in a net lost.

    Edited: Clarify first paragraph
    Reply
  • Blueberries
    16734708 said:
    indeed a PSU's peak efficiency is with typical loads (40-50% of its max rated capacity). However you should also take into account how long your system operates at full load.

    It is absolutely true that power supplies are usually at their best efficiency around 50% of their maximum load, but that doesn't necessarily mean a smaller PSU is better.

    All switching power supplies decrease their efficiencies as their load decreases, typically starting at or near 50% load and often rapidly decreasing efficiencies as their load falls below 20%.

    For desktop systems, unless you run a distributed computation project in the background, 80-95% of the time the system is powered on, the system is idle or near-idle. In my limited testing a desktop system likely draws 50-100W at idle, so with a 1000W power supply it's operating at 5-10% load, and thus at its worst efficiencies.

    With Haswell and newer consumer Intel's CPUs maxing out at 145W (I believe) at stock frequencies, and most video cards needing under 200-250 W maximum (980Ti 250W), a system with a single GPU rarely needs more then 600W.

    Specifying the PS for 50% load (for maximum efficiency) to match the maximum load the system is actually capable of drawing is a poor efficiency trade-off, as the system will spend the majority of time time at under 20% utilization, at its worst efficiency, that the few percentage points of increased efficiency (at 50% load versus moderately higher loads) will result in a net lost.

    Edited: Clarify first paragraph

    Yes but titanium efficiency PSUs retain 90% efficiency at a 10% load and platinum achieve at least 90% efficiency at 20% load. See: https://en.wikipedia.org/wiki/80_Plus

    If the components are good they'll be able to handle a large load. There's no such thing as a good PSU that can't handle a large load. Most platinum PSUs can handle well over what they're rated for.
    Reply