Cann a cosair cx500 handle a hd5850?

Solution
A system with a single HD 5850 requires a 500W PSU with at least 32A on the 12V rail and two 75W 6-pin PCIe power connectors. At full load, this system will consume around 350W.

The Corsair CX500 has 34A on the 12V rails and two 6+2pin PCIe power connectors and is sufficient to power your system. If you plan on OCing the CPU/GPU then I would recommend a PSU with more stout 12V rail(s); something with 40A+ on the 12V rails like the Seasonic M12II-520, Antec HCG 520, or the XFX Core 550W.
A system with a single HD 5850 requires a 500W PSU with at least 32A on the 12V rail and two 75W 6-pin PCIe power connectors. At full load, this system will consume around 350W.

The Corsair CX500 has 34A on the 12V rails and two 6+2pin PCIe power connectors and is sufficient to power your system. If you plan on OCing the CPU/GPU then I would recommend a PSU with more stout 12V rail(s); something with 40A+ on the 12V rails like the Seasonic M12II-520, Antec HCG 520, or the XFX Core 550W.
 
Solution
one question though, what is better single 12V rail or multiple 12V rail? the xfx core 550q has single 12v rail with 44Amps while seasonic m12II-520 has double 12V rail totaling 40Amps
 
There is a lot of debate back and forth, but it doesn't really matter for the average user. I have a Seasonic M12II-520 running an HD 6950 with absolutely no issues; the XFX 550W is made by Seasonic and is also a great little PSU. Bottom line...get either one and be happy with a great PSU.