GTX 560 or HD 6870 with 475w psu?

[Pants01]

I have a Dell studio 435t that has a 475w flextronics stock psu.
Machine came with a i7 2.6GHz, 12g RAM,GTX 260

http://www.txcesssurplus.com/servlet/the-6779/Dell-F217J-Studio-XPS/Detail

Looking at manufacturer sites they say either 450w or 500w minimum recommended psu's for the HD 6870 and the GTX 560.
I don't need to go to a 560ti to get a good performance boost so I was wondering if it's a good idea to run either of these cards with this psu or should I really just buy a new psu too. Trying to get away with not replacing it if possible.

 

[azeem40]

6870, but I wouldn't trust that PSU.

 

[mubin]

6870 require 151w and 560ti require 170w. So 6870 is the chioce, but your psu is tighten and maybe not that good.

 

[scannall]

This is a good way to figure it out, without doing a lot of guessing.

http://extreme.outervision.com/psucalculatorlite.jsp

 

[samuelspark]

Nope. Stock generic PSU? A good 430w can run a 6870 but...

 

[Pants01]

I've seen other posts saying the flextronics psu is good so I don't know why a good 430w would run a 6870 but my 475w won't.
Either way I was just hoping I wouldn't have to get a psu. My wife has the same pc and I'll be doing the same upgrade in both, that's why I was trying to not replace the psu.