Recommended PSU for the following rig ...

Any decent psu with 500W, list the budget, but any psu within 500-600W from brands like antec, corsair,xfx, seasonic,fsp,pc power and cooling,ocz, super flower, etc will do.

For a system using a single reference design Radeon HD 7850 graphics card AMD specifies a minimum of a 500 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 27 Amps or greater and have at least one 6-pin PCI Express supplementary power connector. Some of the non-reference design Radeon HD 7850 graphics cards require at least two 6-pin PCI Express supplementary power connectors.

For a system using a single Radeon HD 6870 graphics card AMD specifies a minimum of a 500 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 33 Amps or greater and have at least two 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.

Overclocking of the CPU and/or GPU(s) will require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.