Two weeks ago we told you that AMD recommends a 750W PSU, but that the Radeon HD 2900XT will work with a high end 400 to 500W PSU as well.
AMD is a legal minded company, so they said that the card should work with any 750W PSU, as many cheap 500W models will fail to power the card. You can read the original story here.
In this 70 page document you can read all about the power connectors and demands, but pay attention to page 6, as AMD suggests you to upgrade the AGP drivers before you install this AGP card. Well done.
And here's the document.