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SilverStone SX550 SFX PSU Review

SilverStone continues to enrich its SFX PSU portfolio. One of the most recent additions is the SX550, a budget-oriented unit featuring Gold-class efficiency and fixed cables instead of modular ones. As you can tell, it's intended to bring prices down.

Efficiency, Temperature And Noise


Our efficiency testing procedure is detailed here.

Using the results from the previous page, we plotted a chart showing the SX550's efficiency at low loads and loads from 10 to 110 percent of its maximum-rated capacity.

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The ACRF topology cannot match more advanced and more expensive designs when it comes to efficiency. The SX550 scores last under normal loads, while under light loads it manages to surpass two SFX-based competitors.

Efficiency At Low Loads

In the following tests, we measure the SX550'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 SpeedFan NoisePF/AC Volts
11.211A0.491A0.471A0.195A19.6368.81%1495 RPM27.8 dB(A)0.859
22.453A0.980A0.977A0.395A39.7479.82%1495 RPM27.8 dB(A)0.953
33.698A1.467A1.485A5.028A59.8484.07%1495 RPM27.8 dB(A)0.973
44.931A1.964A1.965A0.795A79.7086.00%1495 RPM27.8 dB(A)0.976

Under 20 W of load, efficiency drops below 70 percent. We don't like to see this. However, in the next three tests, the SX550 achieves decent efficiency levels. The fan's noise is kept low throughout all low-load tests.

5VSB Efficiency

The ATX specification states that 5VSB standby supply efficiency should be as high as possible, recommending 50 percent or higher 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. 

Test #5VSBDC/AC (Watts)EfficiencyPF/AC Volts
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The 5VSB rail achieves decent performance overall.

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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With a little lower vampire power, the SX550 would attain improved results in our 5VSB efficiency measurements. Be that as it may, this PSU easily meets the ErP Lot 6 2013 directive's requirements with both voltage inputs.

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 38 °C (100.4 °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 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 38 °C (100.4 °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 28 °C (82.4 °F) to 30 °C (86 °F).  

At normal operating temperatures, the SX550 achieves quiet enough operation, especially if we take into account its small dimensions and 80 mm fan. Up to around 200 W, the noise output is under 28 dB(A), while it exceeds 40 dB(A) with higher than 275 W loads. Noise drops again within 37-40 dB(A) for a short period, and with higher than 400 W loads it reaches the 43-46 dB(A) region.

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