High-end graphics cards consume from 75 watts up to 150 watts of power. The PCI Express* x16 connector on Intel® Desktop Boards can deliver only up to 75 watts.
For graphics cards up to 75W
These graphics cards can be powered by just the PCI Express x16 connector on the desktop board.
For graphics cards 75W and greater
These graphics cards usually require extra power, provided by both the PCI Express x16 connector and a 2x3 auxiliary power cable built into power supplies. If you don't connect the extra 2x3 power cable, your system may not boot up.
See the documentation that came with your graphics cards for power supply requirements and details on connecting auxiliary power cables.