On Figure 10 you can see GlacialPower GP-PS550BP label stating all its power specs.

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Figure 10: Power supply label.

As you can see, the +5 V output is labeled as capable of delivering a maximum current of 25 A, what translates into 125 W, and the +3.3 V output is labeled as capable of delivering the same amount of current, 25 A, what translates into 82.5 W. This is below the maximum theoretical power we calculated on the previous page. However GlacialPower states the maximum combined power of the +3.3 V and +5 V outputs is of 130 W (and not 207.5 W, which is 125 W + 82.5 W). This happens because the +5 V and +3.3 V outputs are obtained from the same transformer output, as you can see on Figure 8.

As for the +12 V outputs, this power supply has two rails, +12V1 and +12V2, each one labeled as capable of delivering up to 18 A or 216 W. These rails, however, cannot deliver their maximum current/power at the same time – this happens with all power supplies. The combined limit for the +12 V outputs of this power supply is 400 W. This value is above the maximum theoretical current the +12 V can deliver, as calculated on previous page.

The whole question regarding +12 V rails is the power distribution. The +12 V outputs – i.e. SATA drives, hard disk drives, main motherboard connector, ATX12V and VGA power cables – must be well balanced between the power supply’s rails, or the protection circuits will kick in even if the power supply isn’t delivering its maximum capable power.

On this power supply, for example, each +12 V rail can deliver up to 18 A. If your system pulls over 18 A (i.e. 216 W) on the power supply’s +12V1 output, it will shut down, even if are not using the +12V2 rail. In other words, the power supply will shut down at 216 W even though it is capable of delivering a combined 400 W on its +12V outputs (the over current protection is set at little higher level than what is announced on the product label, but let’s not consider this in the name of simplicity).

We think the power distribution on this power supply isn’t optimal, because the +12V2 rail is connected only to the ATX12V connector, while all other wires are connected to the +12V1 rail. So the +12V1 rail is obviously overloaded, especially because this power supply has two auxiliary PCI Express power connectors for two video cards.

This means that with this power supply you have a high chance of the power supply shutting down due to its over current protection while running a SLI or Crossfire configuration or even when using a single very high-end VGA, not because you have reached the power supply’s maximum power limit, but simply because of the power distribution across the +12V rails.

We think this power supply would have a better design if it had some other components connected to the +12V2 rail or if it had three rails, optimally with the main video card power connector connected to the third rail.

On the other hand GlacialPower says that this unit can deliver its labeled 550 W at 45º C, which is great. Usually power supply manufacturers label their units at 25º C, which is a shame: since the capability of delivering power shrinks with the temperature, usually you can’t achieve the labeled power under real-world conditions if you have a power supply labeled at 25º C.

Unfortunately we don’t have the necessary equipment to make a true power supply review; we would need to create a real 550 W load to check if this power supply could deliver its labeled power or not. In this First Look article we’d like to show only the internals of GlacialPower GP-PS550BP.