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Corsair RM750x PSU Review

Corsair released its RMx PSU line, which the company claims will offer good performance along with silent operation. Unlike the RMi models, the RMx units lack a digital interface, a fan test button, and uses a Rifle bearing fan instead of an FDB version.

Efficiency, Temperature, Noise, Cross-Load Tests And Infrared Images


Our efficiency testing procedure is detailed here.

Using the results from the previous page, we plotted a chart showing the efficiency of the RM750x at low loads, and loads from 10 to 110 percent of the PSU's maximum-rated capacity.

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The RM750x that we had in hand proved to be a little more efficient, compared to the RM750i that we tested awhile ago. Compared to the competition, it scored very well; but it wasn't able to come even close to both Seasonic platforms with a similar capacity.

Efficiency At Low Loads

In the following tests, we measure the efficiency of the RM750x 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.

Test #12 V5 V3.3 V5 VSBPower(DC/AC)EfficiencyFan SpeedFan NoisePF/AC Volts
11.204A0.491A0.480A0.195A19.60W68.58%0 RPM0 dBA0.836
22.437A0.989A0.992A0.395A39.70W79.16%0 RPM0 dBA0.929
33.677A1.476A1.505A0.594A59.81W83.92%0 RPM0 dBA0.960
44.902A1.985A1.988A0.795A79.75W85.82%0 RPM0 dBA0.969

Efficiency at light loads is very good. With 60W and 80W load, the RM750x easily passed the 80 percent mark, and even with 20W load it managed to stay close to 70 percent. Finally, on all of the above tests the unit's cooling fan wasn't engaged, although the ambient was close to 40 C.

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. 

Test #5VSBPower (DC/AC)EfficiencyPF/AC Volts
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The 5VSB rail achieved very good efficiency levels. As you can see from the table above, it managed to score over 80 percent efficiency with 1A load — a result worth mentioning, since very few PSUs are able to pass the 80 percent mark in these tests.

Power Consumption In Idle And Standby

Mode12 V5 V3.3 V5VSBPower (AC)PF/AC Volts
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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 extremely low with both 115V and 230V supply voltage. This plays a key role in the 5VSB rail's high efficiency levels, 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 39 C (102.2 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 soundproofing 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 39 C (102.2 F) to 49 C (120.2 F) ambient temperature. 

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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) to 30 C (86 F). 

We believe that the high load that we applied from the start on the minor rails resulted in a very short passive mode. We noticed the same behavior in the RM750i, so most likely this is a quirk that is specific to this platform. Despite the short passive mode period during our cross-load tests, the PSU managed to operate very silently, overall. 

Cross-Load Tests

Our cross-load tests are described in detail here.

To generate the following charts, we set our loaders to auto mode through our custom-made software before trying more than 1,500 possible load combinations with the +12V, 5V and 3.3V rails. The load regulation deviations in each of the charts below were calculated by taking the nominal values of the rails (12V, 5V and 3.3V) as point zero.

Load Regulation Charts

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Efficiency Chart

Ripple Charts

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Infrared Images

Toward the end of the cross-load tests, we took some photos of the PSU with our modified FLIR E4 camera that delivers 320x240 IR resolution (76,800 pixels).

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We pushed this PSU very hard, as you can see from the thermal shots above. In the worst-case scenario, the operating temperature of several components was well above 70 degrees Celsius (158 degrees Fahrenheit), and the very high temperature didn't seem to affect its performance in any notable way. During our overload test at 49.5 C (121 F) ambient temperature, the bridge rectifier went up to 116 C (240 F). However, that very high temperature didn't pose a problem for the proper operation of this specific component. On the contrary, the higher the working temperature of a bridge rectifier, the lower the voltage drops on its diodes are. Thus, efficiency is increased because less energy is wasted. 

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