[BigV]

the connectors are key, obviously. As is the physical size of the PS, you will need to put it back in the hole made by the old one, obviously.

As for power ratings, you can go as high as you like in the "power rating", (within reason) more is better. a unit rated for higher output will be loafing more under a similar load. but I wouldn't spend more than 1.25 * the price for a higher output PS.

Really, as computer components go, this is about as plug(and plug and plug and plug and plug) and play as it gets. You'll do fine. You might want to let your fingers do the walking to make sure they have one.