Hi, you missunderstood me. The PSU burnt 2 Cards but one after one. After the first Card was burnt (it was 2 years and 2 month old, so 2 months out of warranty) i thought ok, warranty gone card broken...nice....Then i bought a new one (Nvidia), plugged the 2 PCIe 6pin on the card. After 2 Months it was burned and showed the same issue like the first card: 65536 colors only and resolution with maximum of 800x600. So from this moment it was clear for me, it have to be the PSU or the Mainboard. But i was pretty sure that it came from the PSU. So then i used an old card which didnt need extra power supply via PCIe 6 Pin connectors. After more than one year, the card was still running and i was sure it have to be the Corsair PSU. Now i had another card, the GTX 560ti and used it with 2 Molex->PCIe 6 Pin adaters. But that made a cable mess. So i used last days again the 2 6Pin connectors and i have seen in HWinfo, that VIN6 stopped jumping from 1,8 volt upto 2,2 volt and down to zero volt and i would like to now what is going wrong there.If your Corsair 550W PSU fried 2 graphics cards, and you are using Molex to PCIE power adapters to power a 3rd GPU so it doesn't get fried, perhaps you should consider replacing the Corsair power supply! If there is really something wrong with it, I would replace it before it fries something else or fails catastrophically.
Corsair does not design or build power supplies. Like many companies, they buy them from OEM's. Because of this, there is little consistency. Some models are great but others are complete dogs. I don't know exactly which one you have but it sounds like replacing it would be your best move. If you still like Corsair, you can pick up a 550 watt 80 Plus Bronze for between $45 and $85 depending on the model. Probably cheaper if you shop around.