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So I have a couple of EVGA Supernova NEX650G power supplies and even though on paper one of these should be fine running 6 x 750 Ti's (~400W), I concluded that it can't output enough power through it's peripherals/SATA ports so if I start hashing with 6 cards it will restart almost instantly while running only 5 cards works fine - if I don't overclock. The only way I managed to hash with 6 cards (other than using a 850W PSU)  is to replace two of the 750 Ti's with a brand that need 6-pin power so a bit of the power is coming from the PSU's VGA rail instead of the peripheral/SATA rail. But the hashrates are about 85% of what they should be and I can't even overclock. My question is, can I convert the PSU's VGA or CPU2 channel into MOLEX/SATA for the USB risers somehow, or what can I do?

http://screenshotuploader.com/i/1406/4jbm0.png

http://www.evga.com/products/pdf/120-PG-0650-GR.pdf

Sounds like you don't have molex for your riser.

The PSU has 2 peripherals (molex) and 3 SATA ports and they are all being used. Two cards per daisy-chain max. AFAIK USB risers can't work without them being powered anyway.

If anyone wondering...

I've been told it's because the PSU's are being multi rail PSU's and not single rail ones which means it can't output it's full capacity though only the SATA/Molex ports. The 650W capacity is divided over multiple rails so pulling 650W from it would only be possible if I were to use the 6(+2)-pin VGA ports aswell, but I don't need any of those. On a single rail PSU I could pull 650W only using the SATA ports as it would come from the same single rail as the 6(+2)-pin VGA ports.
So now I either butcher the cables and connect the 6-pins to the USB risers (which apparently is only using the 12V line of the SATA/Molex and not using the 5V line) or replace the PSU's. But since I don't feel like tinkering with brand new PSU's and they are terribly loud anyway, I'm going to replace them.