I know a lot has been already said about the right PSU for any given gcard (in this case a 5850) but i still have some questions i would like to have answered before i buy a new PSU.
In other forum posts i have read that for a 5850 a PSU should have at least 500w and something about 12v/40a+ on a rail something...very new at this sorry... Anyway, after researching a bit i came across some PSUs that either had 12v/40a plain and simple in the description (like a corsair) and others that had stuff like 12v1/18a followed by 12v2/18a, 12v3/18a, 12v4/18a...
So my question is, what's the difference? Do the ones that seem to me to have severall "voltage pathways?" add up the diferent paths in the end so it matches or surpasses the 12v/40a single one?
Hope someone can clarify this to me. I have bought a brand new HD5850 and, by the post u can already guess, my PSU couldn't handle it...its a really bad one, no brand really...a white mark one...sigh...so i have the card next to me teasing me for being a noob...
There are multiple rail PSU's which have more than one 12V rail with certain amp rating.. Normally you just add up the respective amp measures to get the total rating.. Some PSU's have single rail system in which a single 12V rail is rated with certain amps.. In either case, multiply the total amp rating with 12 to find out the wattage measure for the PSU.. Beware that the actual wattage supply may differ from the advertised.. This is the reason (along with few others) that a critical component such as the PSU needs to be selected from a reputed brand house..
For your needs, I'll recommend a good 500+ watt PSU from brand such as Corsair or Seasonic.. specifically, the Corsair VX 550 or the Seasonic M12II 520 will be both good and enough..