I recently got a XFX 9600GT XXX Alpha Dog Edition: http://www.overclockersclub.com/siteimages...on/12_thumb.jpg a friend gave it to me in mint condition and plugged it in my computer and noticed a plug at the back for power(six-pin), so i told him should i plug it in? he said depends on my PSU. My PSU is 550Watts, and he said no. i think i should put it in since it's a powerful card Should i plug it in? is it necessary?(tell me the problems if i don't plug it in) btw, this is my first card and its free and the box is nice.