This is an interesting post from there thats a bit more specific and to the point... sorry i cant find the "quote" button in my reply but its below the dotted lines instead hehe
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170W + 600W + 9.6W + 15W = 620 ?
140W + 480W + 9.6W + 15W = 520 ?
How misleading It's actually 620-(170+9.6+15)=425.4w for 12v rails on the 620w unit. This leads to 425.4w / 12v = 35.45a which is enough on the table if this unit can really combine rails. 11.81a for each 3 rail which is ONLY good if a rail only serves the gfx card, nothing else. That's very unlikely, believe me.
It's worse on 520w unit. 520 - (140+9.6+15) = 355.4w and it's 355.4w / 12v = 29.66a for 12v rails. 9.8a for each 3 rail. And it may not even be the sustained(very important) but MAX/PEAK value which means nothing. Even if that unit can combine amps as it's supposed to, it comes short by a few amps. Those a few amps may lead to damage on the card or the psu.
Now, you must be careful about PSUs, because the companies are not always honest with the values or the unit can't live up to the specs. That's a fact, that's always been like this. The amps weren't an issue before because the gfx cards weren't powerful that much, they soon became wattage hungry and then amps hungry. So it's all about whether a unit can provide the rated specs or not. Even decent companies have crap PSUs but at least there're also ppl on internet that you can get info, advice about PSUs, because they just tried hundreds of combinations unlike regular home builders like us. And it's faster than formal ways most of the time.
One more thing. Almost every decent mobo has at least one thermo stick connection. Find one, put it inside the PSU of yours and plug it to the mobo. The default mobo application should show thermo stick temp. See if it's more than 50c or not. Because that 520&620 units are rated best under 50c. Heat is the main enemy of electronics, mostly for PSUs which will be less efficient.
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anyways, thats just one of the numerous posts that go on about that PSU and its suitability to the X1950 card
the whole thread can be found here:
http://www.sapphiretech.com/en/forums/showthread.php?t=14091&page=1&pp=10&highlight=corsair+520