specking your power supply is very important as i found out, since i fried my 800W as i was pulling ay to many amps on the 5V rail. melting smoke aint funny. as a rule of thumb always asume psu are only 80% efficient. so with a 550W dont go above 440W and obviously pay not on the amp rating of the psu as 550W not the whole power supply but more likely 470W only for the 12V rail.
RIP odin....