I have this PSU ....a gift from my brother for my bday
Want to add a 7950 ...just 1 for now
Both good brands once you get above the budget/opening price point
series, and into Enthusiast or Professional models.
As dude said, your build & use determine how much PSU you need.
If you are going with one 7950, then a quality 500w unit is more than sufficient.
If you are def planning to CF down the road, then the 750 mentioned above is
more than sufficient(plenty of headroom for 2 - 7950's).
Assuming you will eventually CF 2 - 7950's and a $140 budget limit,
you might want to consider these: