On Figure 16 you can see this power supply label containing all its power specs.

click to enlarge
Figure 16: Power supply label.

As we mentioned before, this power supply has six virtual rails, with +12V3 and +12V4 labeled with a 28 A maximum current and all the others labeled with an 18 A maximum current.

These rails are distributed as follows:

• +12V1 (yellow with black stripe wire): Main motherboard cable, half of the EPS12V cable.
• +12V2 (solid yellow wire): ATX12V, half of the EPS12V cable.
• +12V3 (yellow with blue stripe wire): 6/8-pin video card power cable.
• +12V4 (yellow with green stripe wire): 6/8-pin video card power cable.
• +12V5 (yellow with red stripe wire): 6-pin video card power cable, peripheral power cables.
• +12V6 (yellow with white stripe wire): 6-pin video card power cable, SATA power cables.

This configuration is probably the best we’ve seen to date. As you can see on this power supply each video card power cable uses a separated rail, with a higher current limit on the rails with the 6/8-pin cable.

The usual configuration on other power supplies with four video card power cables is connecting two cables on one rail and the other two on another rail. If you install two power-hungry video cards on the same rail, the over current protection may kick in shutting down the power supply even if the video cards are just running inside their specs. To prevent this from happening some manufacturers simply disable the OCP circuit (transforming the power supply into a single-rail design) or configure OCP with a value that is too high. In both cases the power supply isn’t offering any kind of over current protection.

This Cooler Master power supply solves this issue by putting each video card power cable on an individual rail, so the power supply won’t shut down if you are running up to four video cards inside their specs but will provide you with over current protection in case something wrong happens.

We tested OCP circuit and it is really active as we will discuss later.

Let’s now see if this power supply can really deliver 850 W of power.