|So then, you have unplugged the main power connector to the motherboard while the power supply had AC current running through it? |
If so, you MAY have damaged the motherboard. I can't say if the capacitors in a PSU are supposed to bulge or not because I haven't dismantled one. That is very dangerous. The capacitors can remain charged for long periods of time and can harm you.
At any rate, PSUs are not a consumer serviceable component.