Recently I looked at a machine for someone with a dead PSU. I put in a second hand cheapie to see if my diagnosis was correct, all I got was a gentle phut and a smell of burning. Turns out my customer had tried to fix it himself and had wrongly wired the case wiring. Sorted that out and fitted a new PSU and away he went. So I'd say that a faulty Mobo can take out a PSU.