Power supply 550W will it be able to run ATI Radeon HD6850?

No that looks like a very cheaply made PSU. It lists 20 I/O but if that is equalivant of Amps, then no. You want to have 35Amps on the +12Volt rail or rails. The 5770 would probally be ok on that one, if you trust it... Ok, I won't suggest you buy a new PSU ever. Keep that one until the rust has taken it away into PSU heaven...