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Seasonic Focus Plus 750 Gold PSU Review

Efficiency, Temperature & Noise


Our efficiency testing procedure is detailed here.

Using results from the previous page, we plotted a chart showing the SSR-750FX's efficiency at low loads, and loads from 10 to 110 percent of its maximum-rated capacity.

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Under normal loads, the Seasonic platform isn't as efficient as its competition. For instance, compared to Corsair's RM750x, the difference is notable. Even the similarly-priced TX750M achieves higher efficiency.

The situation improves under light loads, where Seasonic's platform takes the lead from Corsair's TX750M. However, the RM750x is still ahead of the SSR-750FX.

Efficiency At Low Loads

In the following tests, we measure the SSR-750FX's efficiency 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 SpeedPSU NoisePF/AC Volts
11.205A0.493A0.482A0.195A19.66568.239%0 RPM<6.0 dB(A)0.750
22.433A0.991A0.997A0.391A39.75379.148%0 RPM<6.0 dB(A)0.884
33.665A1.487A1.509A5.106A59.86283.966%0 RPM<6.0 dB(A)0.938
44.880A1.996A1.995A0.780A79.75686.353%0 RPM<6.0 dB(A)0.959

With a 20W load, we would like to see over 70% efficiency. Under 40W of load, it would be nice to go over 80%. But this PSU only breaks the 80% mark in the last two tests. The fan doesn't spin during any of these tests, so noise is kept to a minimum.

5VSB Efficiency

The ATX specification, along with CEC, ErP Lot 3 2014 and ErP Lot 6 2010/2013, states that 5VSB standby supply efficiency should be as high as possible, recommending 75 percent or higher with 550mA, 1A, and 1.5A of load. The PSU should also achieve higher than 75% efficiency at 5VSB under full load, or with 3A if its max current output on this rail is higher than 3A.

We take six measurements: one each at 100, 250, 550, 1000, and 1500mA, 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 isn't as efficient as we expected, particularly since Seasonic typically uses highly efficient 5VSB circuits in its designs.

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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Vampire power remains at very low levels under both voltage inputs.

Fan RPM, Delta Temperature, And Output Noise

Our mixed noise testing is described in detail here.

The chart below illustrates the cooling fan's speed (in RPM), and the delta between input and output temperature. The results were obtained at 37°C (98.6°F) to 47°C (116.6°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 hemi-anechoic chamber. Background noise inside the chamber was below 6 dB(A) during testing (actually it is much lower, but our sound meter’s microphone hits its floor), and the results were obtained with the PSU operating at 37°C (98.6°F) to 47°C (116.6°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 30°C (86°F) to 32°C (89.6°F).  

The fan's passive mode doesn't last long. Then, it spins slowly, remaining in the 10-15 dB(A) range. With more than 490W on the +12V rail, the fan starts to make its presence felt. As the load exceeds 550W, output noise exceeds 40 dB(A). Beyond 620W load on the +12V rail, the situation gets serious, and the fan generates more than 45 dB(A).

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