I installed an nVIDIA/ ATI high-end graphic card which has 2 power connectors (2x 6-pin and 1x 8 pin connector or 1x6) and my computer doesn’t start anymore or turns off after a few seconds.
Our power supplies have 4 separate 12V rails, and adhere strictly to the applicable safety requirements, namely, each 12V line shall not exceed the maximum continuous power output of 240 Watt/20A (depending on model). The power supplies have two 12V rails for the graphics card and have two connection options: either 2 x 6-pin PCI-E connectors or 1x 6-pin and 1x 8-pin (2 +6 Pin) PCI-E connectors. The 12V line is marked on the port with a PCI-E and PCI-E 2.
Please note that if connecting the graphics card with a power supply from 240W up to 400W, the two separate 12V power connectors of the graphics card (PCI-E 1 and PCI-E 2) are used to spread the maximum load on both 12V rails. Otherwise, the PSU won’t start or will turn off immediately due to the protective functions.
The ATI HD 3870 X2 graphics card has 2x 6-pin or 1 x 6 - and 1 x 8-pin PCI-E connectors. The graphics card requires about 370W under load. If you connect the two PCI-I connectors only to 12V1, the PSU will not start or turn off after a short time because one 12V rail will only provide 240W. If you connect the graphics card with the 6-pin PCI-E connector of 12V1 and the 8-pin PCI-E connector of 12V2, your system will run without any problem.