For a system using a single Radeon HD 6570 graphics card AMD specifies a minimum of a 400 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 20 Amps or greater.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important factor.