In Win Classic Series C 900W PSU Review

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Efficiency, Temperature, And Noise


Our efficiency testing procedure is detailed here.

Using the results from the previous page, we plotted a chart showing the C900's efficiency at low loads and loads from 10 to 110 percent of its maximum-rated capacity.

Under normal loads, the C900 comes very close to the competition. With light loads it even manages to take the lead from high-end units like the EVGA 850 P2.

Efficiency At Low Loads

In the following tests, we measure the C900's efficiency under loads significantly lower than 10 percent of its maximum capacity (the lowest load the 80 PLUS standard measures). The loads we dialed were 20, 40, 60 and 80 W. This is important for representing when a PC is idle, with power-saving features turned on.

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Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan SpeedFan NoisePF/AC Volts
11.175A0.481A0.475A0.194A19.6272.56%290 RPM21.2 dB(A)0.808
22.382A0.968A0.982A0.395A39.7782.02%290 RPM21.2 dB(A)0.918
33.586A1.460A1.490A5.008A59.8584.39%290 RPM21.2 dB(A)0.944
44.789A1.962A1.969A0.799A79.8087.53%290 RPM21.2 dB(A)0.974

Efficiency is pretty high under light loads, while output noise is low since the fan barely spins.

5VSB Efficiency

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

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

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Test #5VSBDC/AC (Watts)EfficiencyPF/AC Volts

We wanted to see higher efficiency on the 5VSB rail. Excelliance's standby PWM controller isn't so effective, it seems.

Power Consumption In Idle And Standby

In the table below, 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).

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Mode12V5V3.3V5VSBWattsPF/AC Volts

Phantom power might be much lower than the ErP Lot 6 2013 directive's high threshold, however, it is significantly higher than what we usually measure from modern PSUs.

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 (in RPM), and the delta between input and output temperature. The results were obtained at 35 °C (95 °F) to 46 °C (114.8 °F) ambient temperature.   

The next chart shows the cooling fan's speed (again, in RPM) and output noise. We measured acoustics from one 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 chamber was below 18 dB(A) during testing, and the results were obtained with the PSU operating at 35 °C (95 °F) to 46 °C (114.8 °F) ambient temperature. 

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

This is a very quiet unit, even though it uses a 120 mm fan. The slow-spinning blades, along with a relaxed profile are good for near-silent operation under every condition.

Contributing Editor

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.

  • Dark Lord of Tech
    Does the EVGA P2 series have OTP?
  • Aris_Mp
    newer batches have according to my sources. Older ones didn't have.
  • Johan Kryger Haglert
    Terrible bang for the buck you mean.
  • Dark Lord of Tech
    18741010 said:
    newer batches have according to my sources. Older ones didn't have.

    Thank you much appreciated!!!!
  • falchard
    It's not a terrible buy. If you have a beautiful in-Win case, can you really tell yourself the best PSU for the price should be placed in there?