To test the power supply unit, we will not connect it to an everyday system as we would be unable to know the exact load that we would provide and wouldn’t be able to vary the load. Instead we will use power resistors which are nothing more than normal resistors but capable of consuming a good amount of power. How much power depends on the resistance and capability of the resistor, and can be easily calculated by Ohm’s law (Amperes = Voltage / Resistance, Power = Voltage * Amperage).

Hence for example a 1Ohm resistor attached to the 3.3V line will allow 3.3A through it and consume about 10W of power. When adding two of these resistors in parallel, you double the power consumption and allow 20W to be consumed as you halve the resistance this way. Adding more will increase the power consumption. Of course that is not entirely accurate on paper as the fault tolerance of these resistors is high and almost none are exact to their resistance specifications, but after using them we could calculate how much power each bunch of them would consume accurately. This way we can add fake load to any power supply unit, and on any power line we wish with good accuracy.

For testing the Corsair HX620W, taking into account its design and power specifications, we took the following steps:

Total Load	3.3V Load	5V Load	12V-1 Load	12V-2 Load	12V-3 Load
33% (~200W)	12A (40W)	16A (80W)	3A (36W)	3A (36W)	1A (12W)
50% (~300W)	12A (40W)	16A (80W)	5A (60W)	5A (60W)	5A (60W)
75% (~470W)	18A (60W)	25A (125W)	8A (96W)	8A (96W)	8A (96W)
100% (~620W)	18A (60W)	25A (125W)	12A (144W)	12A (144W)	12A (144W)

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The room temperature when the test took place was 20 Celsius degrees. The performance of the HX620W under these conditions was simply astonishing. The power supply could manage to provide every last watt it was rated for. It could actually provide more power without shutting down, but this was a cool day and power supply units do degrade as they are heated up, so this does not qualify much as a “real-world” scenario.

To test Corsair’s claim that if a 12V line is overloaded power sharing automatically takes place between the lines, we placed a 20A load on a single 12V line of the unit without loading the other two. True enough, the unit kept working without any problem.

The HX620W is not loud when operating under low and normal load; it was actually not audible at all. However if severely loaded, the fan of the unit speeds up quite fast and ultimately becomes intolerably loud at full load. This is not a problem that a common user would face though, as most power supply units of this class barely operate at 50-60% of their capacity under full load.