A good 500W PSU will likely work, but the GTX 570 is a power hog. Nvidia specifies a 550W PSU; the PSU should have a t least 40A on the 12V rails and two 75W 6-pin PCIe power connectors. Most 500W PSUs do not have 40A on the 12V rails. IMO the best PSU in that range that meets the 40A requirement is the Seasonic M12II-520: http://www.newegg.com/Product/Product.aspx?Item=N82E16817151093&Tpk=m12ii%20520
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