If the card has an 8 pin receptacle then you have to connect an 8 pin power plug. Try this site for an adapter.
Hi Folks, Can anybody please help with the following: I have a new XPS8940 with GTX 1660 graphics card but the system will not boot with the graphics card plugged in. I get a message on screen saying "Please power down and connect the PCI power cable(s) to all graphics cards" But there is only one graphics card and one cable and it's connected. Removing the GTX1660 and plugging the monitor into the on-board graphics makes everything else work ok. One strange thing I noticed is that the graphics card has an 8-pin power socket but the power cable from the power supply only has 6 pins. Can anybody else with this set up help me by telling me if their cable has 8 pins or only 6 like mine? Regards.
XPS 8940 won't boot with GTX 1660 card plugged in