be quiet! SFX Power 2 300W Power Supply Review

Efficiency, PFC and Voltage Regulation

Voltage Regulation

To test voltage regulation we load the power supply to five different load scenarios that give an equal spread of load across every single rail. So that means 20% on all rails, 40% on all rails and so on. We then calculate the average deviance of each rail from its expected voltage.

Voltage regulation was impressively strong across all rails for such a small unit, only the irrelevant minus 12 volt rail showed weak performance. The minus 12 volt rail is practically irrelevant because the vast majority of modern PCs no longer use this rail.

Power Efficiency

Power efficiency is measured by calculating actual supplied wattage divided by the wattage drawn at the wall/plug, multiplied by 100 to give a percentage. We then compare that to the particular 80 Plus certification the company claims to see if it meets that. You can see the 80 Plus certifications below, we always test 230v power supplies.

Efficiency was met and exceeded the 80 Plus Bronze baseline by quite some margin, it wasn’t, however, high enough to reach the next certification up: 80 Plus Silver.

Power Factor Correction

Power Factor Correction is the ratio of the real power flowing to the load, to the apparent power in the circuit. The aim of PFC is to make the load circuitry that is power factor corrected appear purely resistive (apparent power equal to real power). In this case, the voltage and current are in phase and the reactive power consumption is zero. The closer the number to one the better as this allows the most efficient delivery of electrical power (Source – Wikipedia).

PFC took a hit at lower loads, most power supplies normally ramp up to 0.95+ from 40% load with only 20% load having the lower readings.