More CM PSU and Results Table



The Chroma DC-loads come with an ATX compatible external printed circuit board where you plug all the different voltage rails of your PSU onto. The thick white wires on the left connect the DC-load with the printed circuit board, the black and red wires are used to read the voltages on the printed circuit board as if it where your computer mainboard. What you can't see are the small pins specially added for scope monitoring, but you can spot the probes right. As you may have noticed, the alternating current power supply cable has been dismantled; the reason behind it is to read out the current flowing through it. An AC clamp-on probe will react on the current flowing through one of the conductors of the cable via an electromagnetism principle, but you may measure only one conductor as once so that's why you have to cut the cable. On the intake and outtake ventilation holes we've also added temp monitoring probes but since our testing schedule was really tight we did not take note of these results.


Busy bees: Geoffrey and Cooler Master’s Technical Marketing Manager René Grau at work

For our tests we tried different load conditions, roughly 50%, 75% and 100% load. We then measured the voltage and current for each volt rail and then calculated the PSU's total output power. Via the Yokogawa WT210 digital power analyzer we had the ability to read out the power factor and the total input power of the power supply, the result of the difference between the output and input power is what we call efficiency. The AC clamp was used to analyze the AC inrush current which can be quite high with high-end PSU's, we also had a look at how fast the PSU boots and how the volt rails are pulled "high" in a stable condition.

Overview of all test results



Focused on efficiency we saw the high-end Cooler Master UCP 900W come out as best. Not a surprise since high-end PSU's really have to be efficient in order to keep temperatures reasonable and noise levels acceptable. With the load at only 500 Watt the PSU scored 90% efficiency which is the best score we could obtain that day. Runner up is the Silent Pro M500 from Cooler Master which had a efficiency score of somewhere in the mid-high 80's, followed by Cooler Master's Real Power 620 which also scored 80% + efficiency.
The Sweex 650W unit had lower efficiency scores then the Cooler Master units we tested, at 76%~79% its not that much worse then the Cooler Master quality PSU's but what was really unsatisfying is that we could not even scale up to the maximum rated output power: at roughly 500W this 650W model shuts down. The story gets even worse for the Stability Power 500W unit, at roughly 400W load this unit began to make a weird noises followed by a PSU shutdown, bad smells and a small wisp of smoke coming out of the blower hole. Just before the shutdown we could measure efficiency as low as 66% which is terrible low and may cause the PSU to burn down at higher loads because of problematic cooling performance (if it did not gave up to you already that is).

Another very unsatisfying result is the power factor of the budget power supplies. The ideal number is 1 (100%), Cooler Master stays very close to that number with their PSU's, the low-end no-name brands however don't seem to have any kind of power factor correction circuit. These numbers are not dramatic since we're talking about a single unit and low current streams, not like heavy machinery and stuff like that, but you should not neglect these results either.

We also performed a short circuit test on each PSU, luckily the OCP was working well enough and none of the test samples died in the process.



The above charts show you the output power and PSU's efficiency, with each of the PSU's rated for at least 500 Watt or more it is remarkable how the Cooler Master units have no problem to keep the efficiency up while increasing the output power. Over 400W load the no-name power supply's have either stopped working or have significant lowered efficiency, again I remember you that you should not take into account the scores of the Real Power 620 loaded with 850Watt because we were using the power supply way out of specs.

Focusing on the 50/75/100% load and efficiency we get this:



But there is more, let us have a look at some of the extra tweaks Cooler Master has added just to make sure they deliver a quality product ->