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.
Our hold-up time tests are described in detail here.
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.
For details on our inrush current testing, please click here.
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 V||5 V||3.3 V||5 VSB||DC/AC (Watts)||Efficiency||Fan Speed||Fan Noise||Temps (In/Out)||PF/AC Volts|
|1||2.765A||1.964A||1.964A||0.995A||54.74||82.48%||1495 RPM||27.8 dB(A)||39.75 °C||0.971|
|2||6.589A||2.960A||2.959A||1.200A||109.73||87.45%||1495 RPM||27.8 dB(A)||39.83 °C||0.982|
|3||10.764A||3.466A||3.479A||1.405A||164.83||88.87%||1690 RPM||32.2 dB(A)||40.94 °C||0.991|
|4||14.947A||3.974A||3.978A||1.615A||219.79||89.27%||1860 RPM||36.1 dB(A)||41.53 °C||0.996|
|5||18.798A||4.979A||5.000A||1.823A||274.70||89.14%||2140 RPM||40.4 dB(A)||42.22 °C||0.998|
|6||22.666A||6.000A||6.029A||2.035A||329.70||88.79%||2560 RPM||39.7 dB(A)||43.27 °C||0.998|
|7||26.554A||7.020A||7.065A||2.249A||384.67||88.21%||2810 RPM||42.3 dB(A)||43.90 °C||0.999|
|8||30.476A||8.061A||8.118A||2.462A||439.59||87.43%||3140 RPM||45.5 dB(A)||44.15 °C||0.999|
|9||34.901A||8.585A||8.669A||2.468A||494.62||86.62%||3345 RPM||48.7 dB(A)||44.75 °C||0.999|
|10||39.322A||9.113A||9.208A||2.582A||549.41||85.61%||3345 RPM||48.7 dB(A)||45.90 °C||0.999|
|11||44.405A||9.131A||9.232A||2.586A||604.18||84.61%||3345 RPM||48.7 dB(A)||46.50 °C||0.999|
|CL1||0.097A||14.021A||14.002A||0.000A||116.14||80.91%||2605 RPM||40.0 dB(A)||43.88 °C||0.985|
|CL2||44.965A||1.003A||1.003A||1.000A||542.78||86.78%||3345 RPM||48.7 dB(A)||46.12 °C||0.999|
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.