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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.

Load Regulation, Hold-Up Time And Inrush Current

To learn more about our PSU tests and methodology, please check out How We Test Power Supply Units. 

Primary Rails And 5VSB Load Regulation

Load Regulation testing is detailed here.

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Hold-Up Time

Our hold-up time tests are described in detail here.

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Despite the bulk caps' low combined capacity, the SX550's hold-up time easily surpass the ATX spec's requirement thanks to the ACRF topology. In addition, the power-good signal drops well before the rails go out of spec.

Inrush Current

For details on our inrush current testing, please click here.

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Inrush current is normal with 115 V input and a little higher than expected with 230 VAC.

Load Regulation And Efficiency Measurements

Our first set of tests reveals the voltage rails' stability and the PSU's efficiency. The applied load equals (approximately) 10 to 110 percent of the power supply's maximum in increments of 10 percentage points.

We conducted two additional tests. During the first, we stressed the two minor rails (5 V and 3.3 V) with a high load, while the load at +12V was only 0.1 A. This test reveals whether a PSU is Haswell-ready or not. In the second test, we determined the maximum load the +12V rail could handle with minimal load on the minor rails. 

Test #12 V5 V3.3 V5 VSBDC/AC (Watts)EfficiencyFan SpeedFan NoiseTemps (In/Out)PF/AC Volts
12.765A1.964A1.964A0.995A54.7482.48%1495 RPM27.8 dB(A)39.75 °C0.971
12.002V5.081V3.359V5.007V66.3744.02 °C115.1V
26.589A2.960A2.959A1.200A109.7387.45%1495 RPM27.8 dB(A)39.83 °C0.982
11.970V5.063V3.343V4.988V125.4844.66 °C115.1V
310.764A3.466A3.479A1.405A164.8388.87%1690 RPM32.2 dB(A)40.94 °C0.991
11.961V5.051V3.331V4.970V185.4846.05 °C115.1V
414.947A3.974A3.978A1.615A219.7989.27%1860 RPM36.1 dB(A)41.53 °C0.996
11.949V5.034V3.316V4.949V246.2246.97 °C115.1V
518.798A4.979A5.000A1.823A274.7089.14%2140 RPM40.4 dB(A)42.22 °C0.998
11.929V5.017V3.298V4.931V308.1747.82 °C115.1V
622.666A6.000A6.029A2.035A329.7088.79%2560 RPM39.7 dB(A)43.27 °C0.998
11.909V5.000V3.282V4.908V371.3249.04 °C115.1V
726.554A7.020A7.065A2.249A384.6788.21%2810 RPM42.3 dB(A)43.90 °C0.999
11.886V4.981V3.268V4.887V436.0949.99 °C115.1V
830.476A8.061A8.118A2.462A439.5987.43%3140 RPM45.5 dB(A)44.15 °C0.999
11.852V4.963V3.252V4.867V502.8150.52 °C115.1V
934.901A8.585A8.669A2.468A494.6286.62%3345 RPM48.7 dB(A)44.75 °C0.999
11.806V4.951V3.241V4.854V571.0051.58 °C115.1V
1039.322A9.113A9.208A2.582A549.4185.61%3345 RPM48.7 dB(A)45.90 °C0.999
11.755V4.937V3.225V4.838V641.7653.85 °C115.1V
1144.405A9.131A9.232A2.586A604.1884.61%3345 RPM48.7 dB(A)46.50 °C0.999
11.643V4.929V3.216V4.826V714.0655.02 °C115.1V
CL10.097A14.021A14.002A0.000A116.1480.91%2605 RPM40.0 dB(A)43.88 °C0.985
11.984V4.949V3.256V5.004V143.5550.11 °C115.1V
CL244.965A1.003A1.003A1.000A542.7886.78%3345 RPM48.7 dB(A)46.12 °C0.999
11.776V5.013V3.296V4.938V625.4554.14 °C115.1V

Load regulation is mediocre on all rails and efficiency isn't particularly impressive under high operating temperatures. The SX550 manages to meet the 80 PLUS Gold requirements under 20 percent load. With 50 percent, it lands 0.86 percent away from the 90 percent target. The measurements get even worse under full load as efficiency drops below 86 percent. Obviously increased temperatures have a significant impact on the ACRF topology's performance.

With up to 20 percent load the fan's acoustic output is very low. Noise exceeds 40 dB(A), becoming noticeable especially to sensitive users, when the load level reaches 50 percent. With the fan spinning at close to 3350 RPM, the fan's noise doesn't exceed 50 dB(A). The fan profile definitely isn't aggressive, and the truth is that the small-diameter fan and moderate efficiency levels don't leave much room for a more relaxed ramp.

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