Watts is Amps x Volts. I am going to assume you are talking about a PC power supply. but then I cant for the life of me figure out why you'd be asking about volts? most modern supplies will operate off 115-230V. So you can see Watts are INDEPENDENT of volts
I just gave the simple answer here because that's all that was really needed, lol.
LOL. I know you did. I kinda wanted to point him back to your post/wiki link. but I can't imagine why he'd ask if it wasn't about input voltage? since output voltage is constant. but then I can't imagine why he'd ask that question anyway. lol