Cooler Master G550M 550W Power Supply Review

Today we spend our time with a computer power supply from Cooler Master that is towards the lower end of the wattage scale coming in at 550 watts. Cooler Master claims "notably higher efficiency and voltage stability than other designs." We will see if its Bronze efficiency G550M PSU will stand up to our gauntlet and its own claims.



The Cooler Master G550M is the first power supply we have seen from the GM series that Cooler Master produces so we have a lot of hope for this product. However, previous products that we have seen in similar market segments from Cooler Master have been rather poor offerings. On the flipside, when we have seen products that were in higher tiers the products have been at least good to very good. Therefore, our real question today will be; can Cooler Master turn in a mainstream product that is a good product? Or, are we looking at another swing and miss today? Let's see.

HardOCP’s testing methodology is intended to very much push power supplies to their advertised wattage rating in temperatures that will represent some of the hottest computer enthusiast cases. So if a unit passes all our testing it is definitely not something to take lightly. In fact we expect more power supplies to fail our testing than make it through unscathed.

Build Quality

Starting things off today, we have the build quality of the Cooler Master G550M. Overall, the build quality of the G550M leaves a good bit to be desired as the exterior of the unit even starts things off on a bit of a mixed foot. While the majority of the exterior build aspects are very nice, the non-Flex Force sleeving leaves something to be desired as was the case when we saw the V650S which this unit takes after in cosmetic aspects. When we move to the interior, things move from somewhat mixed to decidedly less good. The actual design is not extremely dated but it is an older design. The integration is generally OK but there were a couple of issues like a few bad touch ups in the soldering. So far, things are in the OK column but when it comes to component selection things get much worse as the capacitors were provided by CapXon and JunFu and the fan was from Yate Loon (which actually helps move things up a bit). Beyond that, the support for this unit is good with a 5 year warranty but the documentation is wretched as always. All in all, the G550M is starting off more like the GX / GXII series and other mainstream/entry level units we have seen from Cooler Master than their better higher end offerings.

Load Testing

The load testing results for the Cooler Master G550M were generally in specification but not as competitive as we would hope for those to be today. During our regular load tests, the G550M saw decent voltage regulation where the 12v rail had a peak change of 0.26v and the minor rails saw peak changes of 0.13v. While passing in the absolute sense of the word, these results, unfortunately, put this unit in the back of the pack of temporal and price comparable units as it trails the Seasonic S12G-550, the Thermaltake Toughpower Gold 550W, and the Corsair CS550M. So, the G550M is getting off to a bit of a slow start. Unfortunately, the efficiency values aren't going to help it catch up any as this unit is advertised as just being an 80 Plus Bronze unit. When we look at the efficiency values that it posted in our load tests, we see that at 120v AC input they ranged from 81.39% to 86.66% and at 100v input the efficiency values ranged from 79.36% to 85.32%. Now, when we look at the actual 80 Plus loads we see that the G550M posted efficiency values of 81.90%-85.97%-81.09% which means that it missed the 80 Plus Bronze cutoffs at 20% and 100% load (that certainly is not helping it compared to the more efficient units that it competes against in the market). Lastly, the unit passed our Torture Test and that combined with the units overall pass does indeed make this unit better than what we have seen from other Cooler Master products that fall in a similar market position and that improvement should be applauded.

The Transient Load Test results for the Cooler Master G550M are passing and good overall. That said, these results do also present us with a bit of an issue when we compare them to other units. Overall, we saw a peak change on the loaded 12v rail of ~250mV while the loaded 5v rail dropped by up to ~110mV. While this unit did trail the Corsair CS550M and the Thermaltake Toughpower Gold 550W it nearly swept the Seasonic S12G-550. Certainly the 12v loaded value is very good and better than what we see from the vast majority of units. Therefore, it is the OK to good result on the loaded 5v rail that side tracked what would have been a dominate performance for this unit today. Instead, this unit is passing but only in the mix rather than rising to the top of the fray as it could have done.

DC Output Quality

In the DC Output Quality portion of testing, we see the G550M sort of stuck in the same rut it has been in. While the G550M starts out well enough, it does see the trace amplitudes on all of its main output voltages increase by a good bit. Indeed, the peak values that we see in our testing are ~40mV on the 12v rail and ~20mV on the minor rails. While in specification, that means that this unit was only able to end mixed compared to the Corsair CS550M and then trailed the Thermaltake Toughpower 550W and Seasonic S12G-550. Unfortunately, coming in at the rear of the pack with the CS550M is not going to make this unit a product that screams "Buy me!". That has been sort of the theme of the day when it comes to test results for this unit.


When it comes to the noise output for the Cooler Master G550M, we see a product that is not likely to be as quiet as some of the other offerings we have seen in this capacity range. This is due to the fact that, while this unit has a large overhead fan, it has rather low efficiency by modern standards and it has low quality components. So, Cooler Master is going to have to keep that fan moving in order to keep those components cool. So, when we tested this unit it was not that surprising that the G550M seemed to have a very steep ramp in noise output that occurred when we started to put the screws to it. Indeed, during the first 75% of the G550M's capacity this unit was not very apparent in our load tests but that all changed rather rapidly when we went above that level. During the Torture Test and the full load test this unit certainly had the fan working at a very good clip and that was apparent in our load testing environment. So, users who are looking for a very quiet, or even just a quiet, option are likely to find better units out there than the G550M from many sources.

Paul's Thoughts:

The Cooler Master G550M doesn't end up being a very competitive product compared to other units you can buy in the same price and capacity range. Heck, it doesn't end up even being a good product at the price tag that it is carrying. However, it does represent a better product than the other kinds of units that we have been seeing from Cooler Master in the mainstream and "gaming" segment that was previous represented in our reviews by the GX and GXII series. In that aspect, the G550M is a great improvement as Cooler Master finally seems to have a product line that most consumers could pick up off the shelf and at least have a reasonable expectation of it being a not dreadful performer in the most average of average builds. Now, given some of the component choices made today some may question the longevity of the unit and that is a valid concern. However, Cooler Master has a 5 year warranty and that warranty is certainly more comparable to what you get from Seasonic with the S12G-550 and Thermaltake with the Toughpower Gold 550W than the 3 year warranty that you get from Corsair with the CS550M. So, it will make most people feel a bit better about some of the design and component selections today.

What would make people feel even better than that though would be for the replacement for this line in the future to use even better components and design choices at the same price point negating that entire issue. In the grand scheme of things though, this seems unlikely to change. If you look back at all of the Cooler Master units we have seen, Cooler Master products seem to fall in two very different categories. Those which are aimed at the top of the market and provide very good performance and even value at times followed by, well, all of the leftovers. The Cooler Master product line up over the years has played out like Twins, just not the normal kind.

The Bottom Line

The Cooler Master G550M is a "Passing" power supply that is better than what we have seen from similarly positioned products from Cooler Master previously. However, the results it posted were never great in any category in our evaluations today. For instance, the voltage regulation was just OK, the efficiency is low for modern standards, and the DC Output Quality is just "good" but not separating this unit from the rest of the pack. The component selection for the unit was not something that screams quality and this unit suffers relative to the price comparable 550W units badly. Indeed, this unit spent most of it's time fighting with the Corsair CS550M and that was not a quality product when we saw it some time ago. That means the G550M isn't going to be one either.

Given that this G550M unit is currently listing for $59.99 after $20 MIR, users would probably be better off looking to products like the Seasonic S12G-550, Seasonic G-550, or Thermaltake Toughpower Gold 550W which can all be had for the same price or less depending on sales pricing. There quite simply is no reason that users should be paying the same price for this Cooler Master G550M PSU as they are for those far and away better options.

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Cooler Master G550M 550W Power Supply