Efficiency

Using the efficiency results from the previous page, we plotted a chart showing the efficiency of the PowerX-550 at low loads and at loads equal to 20-110% of the PSU's maximum rated load.



News are good at low loads, since the unit marginally surpassed the 80% mark. For a Bronze-certified PSU, efficiency is at good levels with normal loads, although we have encountered PSUs belonging to the same category with higher efficiency.

Efficiency at Low Loads

In the next tests, we measured the efficiency of the PowerX-550 at loads much lower than 20% of its maximum rated load (the lowest load that the 80 Plus Standard measures). The loads that we dialed were 40-, 60-, 80-, and 100 W (for PSUs with over 500 W of capacity). This is important for settings where the PC is in idle mode with power saving turned on.


At low loads, even with higher than 35°C ambient, the PSU is very quiet, almost inaudible, at least to our ears. Efficiency is also high enough considering that this is a plain Bronze unit, not a Gold or Platinum one. The fact that it manages to score a reading of nearly 75% with a mere 40 W load is enough to satisfy us, but the PowerX-550 doesn't stop there and scores over 80% efficiency with a load of 60 W and onward. Its low capacity does, naturally, influence its efficiency in a positive way.

5VSB Efficiency

The ATX spec states that the 5VSB standby supply's efficiency should be as high as possible and recommends 50% or higher efficiency with 100 mA of load, 60% or higher with 250 mA of load, and 70% or higher with 1 A or more of load.

We will take four measurements: one at 100, 250, and 1000 mA each, and one with the full load that the 5VSB rail can handle.


At 5VSB, efficiency is high enough overall—easily surpassing the corresponding threshold in every case. It even reaches 80%, a reading not so easily achieved on this rail, with a full load.

Power Consumption in Idle & Standby

In the table below, you will find the power consumption and the voltage values of all rails (except -12V) when the PSU is in idle mode (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).


Phantom power is significantly lower than the 0.5 W limit that the ErP Lot 6 2013 directive sets, which means this unit doesn't waste precious energy, even in standby mode.

Fan RPM, Delta Temperature and Output Noise

The cooling fan's speed (RPMs) and the delta difference between input and output temperature are illustrated in the following chart. The following results were obtained at 38-45°C ambient.



A chart that shows the cooling fan's speed (RPMs) and the output noise follows. We measure the fan's noise from 1 meter away—inside a small custom-made anechoic chamber with internals that are completely covered in specialized soundproofing material (Be Quiet! Noise Absorber Kit). Background noise inside the anechoic chamber was below 30 dBA during testing, and the results were obtained with the PSU operating at 38-45°C ambient.



The following graph illustrates the fan's output noise throughout the entire operating range of the PSU. The same conditions of the above graph apply to our measurements, but the ambient in this case was between 28 and 30°C.