Raidmax do make some really really poor power supplies, but describe what you mean by "frying the motherboard" though.
Yes, sorry about the poor description. When It burns out, it shuts the system down. When you try to power it back on, power gets supplied (case fans/ lights come on) but that's it.
Each time he replaced the MoBo it would power on for several minutes, before the same thing happens again.
edit: I have been informed that the latest MoBo casualty has blinking LEDs that correspond to the code: processor is in 3 phase power.