HD radeon 6850

Hi guys, I currently have a system with the following specs: Dell Optiplex 790 Intel Core i5-2400S DDR3 (4x2 = 8GB) 2 HDDs I've recently got Radeon HD 6850 (Power Color Edition) from one of my friends just to see if I can run/test it in my system. GPU has 6-pin connector, but my PSU doesn't...