Yeah, dude, that happened to me... one hell of a bang, turned out to be the PSU and thankfully didn't damage anything, except the modem which hasn't been entirely normal since. Hope it ain't major.
I drove 60 miles to moms house to give her a Dell I spent two nights loading Windows on and various programs. Plugged it into her wall and the sparks flew out the back like the 4th of July!
Well double crap, the dumb old Dell uses a proprietary power supply plug to the mobo that I can't find. So that's a heap of trash now.
I once plugged a machine in (without cover on) and watched its AMD K6 processor (a true racing car of a chip at the time!) become a pillar of smoke and fire. Luckily it was not actually my machine, I was a technician at the time. Still, ouch.