Power Supply ?????????

I have a Sept. 2004 GX270 tower case.

 

I would like to replace my power supply along with my video card.  I want to upgrade to an Nvidia 6800GT 256mb.  This requires at least a 350watt PSU.  (The factory installed a 250watt.)

 

1. Can I buy a PSU off the "shelf" at Frys, Tigerdirect.com, Newegg.com etc. and install it? and have it work?

 

2. Are the dell Power Supplies for the GX270 wired specially for dell motherboards?  By this I mean are the 20 pin connectors different from those from "off the shelf" PSUs? 

 

 

I know about the one at PC Power and Cooling but I don't really want to spend $130+ on a PSU when there are very good ones for $50.

 

Any help will be greatly appreciated.