Depends on the exact PSU model and the manufacturer.. A good 500W PSU is surely plenty for your setup.. By good I mean from brands like Corsair, Antec, Seasonic etc..
For a system running a single Radeon HD 5830 a reputable name brand power supply with 500 Watts or greater and with a minimum +12 Volt current rating of 30 Amps or greater is recommended. The power supply should also have at least two 6-pin PCI Express Supplementary Power Connectors.