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Cooler Master RealPower RS-550-ACLY

Cooler Master isn’t a brand that you normally associate with power supplies, but recently Cooler Master has expanded its product portfolio to more than CPU coolers and cases. The RealPower models are at the top of the range and available in either 450 or 550W flavours.

We tested the 550W unit and it proved to be nothing short of impressive. It is the most efficient PSU at 25 per cent load in this test and the only one to have over 80 per cent efficiency at such a low load. It is the second most efficient PSU on test here, only beaten by Seasonic, which goes to show that a newcomer can give the established companies a run for their money.

The PSU itself is pretty generic looking, with a black case and a 120mm fan – with blue LEDs of course – so nothing out of the unusual here. However, internally the RealPower is different to all the other PSUs on test by having three 12V power rails. The downside is that they are rated at 12A, 12A and a mere 6A, but as with the Akasa it all depends what is wired to the various rails. As Cooler Master didn’t supply this information it is hard to tell how good or bad this setup is, but it worked well enough in our test.

There are plenty of connection options, but a mere six Molex connectors spread over two cables – one terminating in a floppy connector – is rather disappointing on a 550W PSU. Even more so as it seems that Cooler Master is targeting entry level workstation and server markets with this model. The reason for this is because it has an SSI connector which is needed for some of the latest dual processor workstation and server motherboards.

There is also an eight-pin +12V connector which so far has mainly been for dual CPU systems, although it has made its appearance on some of the latest Pentium 4 motherboards with dual core support. More common connectors included are the four-pin +12V, PCI Express graphics card and three SATA connectors – on one cable. The main power connector is of the 24-pin EPS verity with a suitable adaptor in the box for use with 20-pin ATX connectors.

If you need more than three SATA power connectors an adapter is provided that adds a further two at the expense of a Molex connector. Rather interestingly the RealPower comes with an analogue Wattage meter. This displays the total power consumption of your PC, i.e. the input Wattage, not the output Wattage. However, it is quite hard to read the display as the backlight is quite dim and the scale isn’t very clear. But it is at least fairly accurate, although the higher the system load, the less accurate the read out is.

The voltages are pretty good, although the 5V rail drops quite low at 75 per cent load or higher. The PFC isn’t as good as some of the other units on test with active PFC, but this is really a minor issue. More disappointing is the fact that it only passed the 1kV Hi-POT test and not the 1.5kV test, something Cooler Master can hopefully improve upon in the future.

All in all, the RealPower is a very good power supply and it can be used with pretty much any motherboard. It is fairly pricy at £78.78 but it is one of the best PSUs on test.


Cooler Master is a newcomer to the PSU market, but with the RealPower range Cooler Master shows that it is here to stay. It’s not cheap, but you do get a very good power supply for the money.

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