For a system
using a single Radeon HD 6870
graphics card AMD specifies a minimum of a 500 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 30 Amps or greater
and have at least two 6-pin PCI Express supplementary power connectors
A combined +12 Volt continuous current rating of 30 Amps or greater should be enough to handle a system using factory or manually overclocked Radeon HD 6870 running Furmark GPU stress testing.
Seasonic X-Series 560W (SS-560KM)http://www.newegg.com/Product/Product.aspx?Item=N82E16817151098