My brother had a power supply that did the same. In his case, the 3.3V and 5V rails were a bit low. As a result, his computer would often hang, especially if the video card started drawing a lot of extra power (using the external molex connection).
After replacing the power supply, his computer hasn't hung since.

If your friend is having strange computer problems, or forsees using hardware with high power requirements, I would suggest returning the power supply and getting something more stable if possible.