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Corsair CX650M PSU Review

Corsair's CX series consists of both non-modular and semi-modular units. It was recently upgraded with new members and improved versions of older ones. The CX650M is the third strongest member of the line, featuring 650W capacity and a 40°C rating.

Efficiency, Temperature, And Noise


Our efficiency testing procedure is detailed here.

Using the results from the previous page, we plotted a chart showing the CX650M's efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.

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Compared to Gold-rated power supplies, the Bronze-class CX650M doesn't stand a chance when it comes to efficiency performance. But as you can see from the comparison graphs above, it is way ahead of the similarly-rated Antec VPF650. With a little tuning, the CX650M could meet the 80 PLUS Silver requirements as well.

Efficiency At Low Loads

In the following tests, we measure the efficiency of the CX650M at 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 80W. This is important for representing when a PC is idle, with power-saving features turned on.

Test #12V5V3.3V5VSBDC/AC (Watts)EfficiencyFan SpeedFan NoisePF/AC Volts
11.205A0.491A0.484A0.195A19.6664.16%840 RPM27.7 dB(A)0.905
22.433A0.990A1.000A0.391A39.7476.01%840 RPM27.7 dB(A)0.953
33.669A1.487A1.515A5.085A59.8981.38%840 RPM27.7 dB(A)0.969
44.887A1.987A2.004A0.784A79.7283.82%840 RPM27.7 dB(A)0.977

Efficiency under light loads isn't impressive, that's for sure. However, it's satisfactory for an 80 PLUS Bronze unit. Our only complaint is the fan's speed, which could be much lower under such light loads. The fan isn't noisy, but it could be totally inaudible if Corsair dialed it down to 400 or 500 RPM.

5VSB Efficiency

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

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

Test #5VSBDC/AC (Watts)EfficiencyPF/AC Volts
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The 5VSB rail is a nice surprise because of its high efficiency levels. It truly looks like CWT/Corsair equipped the CX650M with a very capable 5VSB circuit, which puts to shame the corresponding converters of much more expensive PSUs.

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).

Mode12V5V3.3V5VSBWattsPF/AC Volts
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Phantom power is really low, allowing for high efficiency at 5VSB under 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 (in RPM), and the delta between input and output temperature. The results were obtained at 34 °C (93.2 °F) to 45 °C (113 °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 34 °C (93.2 °F) to 45 °C (113 °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).  

Up to around 330W, the PSU operates quietly. It'd be even more so if the minimum fan speed was lower. Above 390W loads, the fan speed increases and so does the noise. In a worst-case scenario, output noise is in the 43-46 dB(A) region, which is pretty loud.

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