I mean, 500W is ok, TDP 955 (teoretical is 125W, but no real, real max is about 105W in burn), HD3870 is about 100W in burn, and 2 modules RAM +2x HDD not too much.
In reviews testers had ussually 600W PSU but high-end GPU gtx265 and more or HD4870 or hd4870x2.