Efficiency

Using the efficiency results from the previous page, we plotted a chart showing the efficiency of the GX-S550 at low loads and at loads equal to 20% -100% of the PSU's maximum-rated load.



The unit's efficiency with light loads is satisfactory since it is close to the average of this category. With normal loads, things are slightly better as the affordable GX-S550 is more efficient than the Super Flower Gold Leadex model.

Efficiency at Low Loads

In these next tests, we measured the efficiency of the GX-S550 at loads much lower than 20% of its maximum-rated load (the lowest load the 80 Plus Standard measures). The loads we dialed were 40 W, 60 W, 80 W, 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.

For its price, efficiency is pretty high at light loads. We would be wrong to ask for better efficiency with light loads, but a more relaxed fan profile at high operating temperatures would be nice. The fan spun very fast even at such light loads (but with ambient temperatures above 39 °C).

5VSB Efficiency

The ATX specification states that 5VSB standby supply 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 the 5VSB rail can handle.

The 5VSB rail isn't that efficient.

Power Consumption in Idle & Standby

In the table below, you will find the power consumption and 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 very low.

Fan RPM, Delta Temperature & 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 °C - 45 °C ambient.



A chart that shows the cooling fan's speed (RPMs) and its output noise follows. We measure the fan's noise from one meter away, inside a small custom-made anechoic chamber whose internals are completely covered in specialized soundproofing material (Be Quiet! Noise Absorber Kit). Background noise inside the anechoic chamber was below 20 dBA during testing, and the results were obtained with the PSU operating at 38 °C - 45 °C ambient.



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



Under normal operating temperatures, this unit is pretty quiet overall. Noise output stays below 28 dB(A) with up to medium loads and never exceeds 40 dB(A).