Right now, I'm running a HD4850 on a chieftec APS 400-s PSU, which has 400W of power and 18A on the 12v rails.
Got an intel e7200 cpu, 4 DDR2 ram sticks and 2 hard drives.
I don't mean to overclock the gpu and was wondering if my gpu would even run on this gpu.
EDIT... I just realized you were looking for a video card upgrade also from your 4850, missed that in your titles. the post bellow is correct, if you go to a 6850, you want to upgrade to a more powerful PSU.
With Just 18A On your !2V Rail, Power = 12 * 18 = 216W Only.
Running A Dual Core E7200 And ATi 6850 On That Will Blow Off Your PC Soon Enough.
Please Upgrade Your PSU To Something Like An Antec,Corsair, Cooler Master.
I Would SUggest The Corsair 500VX2 - 80 Plus Certified!
Or If You Are Low On Budget, Try To Get A Seasonic PSU!