Efficiency

Using the efficiency results from the previous page, we plotted a chart for the HGX550's efficiency at low loads and at loads equal to 20% -100% of the PSU's maximum-rated load.



Efficiency under light loads is high enough, and the HGX550 can compete with other high-end 550 W PSUs well at normal loads. We believe that the native cables and design play an important role in terms of efficiency because voltage drops on modular cables are higher, making PSUs with modular cables slightly less efficient, and most high-end PSUs today are fully modular.

Efficiency at Low Loads

In the next tests, we measured the efficiency of the HGX550 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.

The fan spins at very high speeds at even light loads. The fan should stay well below 1000 RPM in such a situation. Efficiency, on the other hand, is pretty high, easily surpassing the 80% mark.

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.

This is one of the most efficient 5VSB rails we have ever come across. Efficiency at full load nearly peaks at 84%, which is impressive. FSP's claim that their 5VSB rail is very efficient is definitely true.

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).

At only 0.12 W with 230VAC input, vampire power is very low. Vampire power will even be lower with 115VAC.

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 38-45 °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 38-45 °C ambient.



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



At normal ambient temperatures, the fan operates at an almost constant 1200 RPM throughout the PSU's entire operating range. The fan's profile is definitely messed up since it not only starts the fan at a very high speed, but also never adjusts the fan's speed to cool the PSU down as efficiently and quietly as possible. FSP's engineers should find another place for the fan-control thermistor.