PSU price differences vs performance

Solution
Thay have the 750 Watt version marked down 30 bucks and the 650 version just marked down 10 bucks that's the price difference.
Having some extra power you don't need don't hurt and the RMx is a good power supply.
as said below sometime vendor have better sales on units some time to clear out older units when a newer unit may be replacing it. when you look at power supply you have to look at reviews that tear down the units and load test them. those reviews tell you what caps are used and parts. chinia caps low cost power supply...jap caps are used on better built supply.