I seen two computers on fire.

1st, when I was the AG's office a computer tech accidentally plugged the power supply from a Racal Vadic modem into the AT keyboard port of an AST 286 PC. The male plugs were EXACTLY the same. It made a small explosion when it blew out the motherboard. I felt bad for the guy.

The other, I did myself a couple of years ago. I replaced the power supply in my HP Media Center with a generic and the power pins were kind of shoddy. The little protectors on the pins wouldn't stay in place to well and I got careless and two of the raw wires touched and my motherboard burned and took out one of the hard drives when it died.