Should be little scribbles on your power supply called letters. And those letters together are words.
He doesn't have to open up his computer, why would he do that?
How to check? sorry i don't know to much about computers.
If you have specs on your computer, like mine has a sticker on the side, it might say there. If not, google the model of your computer followed by power supply. Mine has 220w and runs the card fine.