Being a computer dumbass, I have no clue how I would find my PSU wattage n' stuff. Halp.
EDIT: I saw those video cards. No cons. *insert gay voice here* Faaaabulous!I guess Nvidia. I heard they're both good.
Edit: Bump cause I'm an starfish.
Open your case (while it's off, lol), check the sticker on the side of the box that has a power cord connecting to it on the outside. Should be on the top or bottom. Look for "Maximum Wattage" or something like that, and while you're at it, look for something that looks like +12V and write the number of Amps, it'll look like this for example:
+12V
-------
23A
If you have multiple 12v rails, it'll probably be something like this.
+12V
1 +12V
2 +12V
3
24A 23A 25A