if it s a good 400w it should run a 390 with a low cpu
i run my 390 with an athlon 620 what use 90w on a corsair cx430 (died after 5 month) when i realize the 12v rail only pull out 336w when it was actually using close to 400w
i run 4x 270 on corsair 650 (600w on 12V) for a year before modify the ring (now i have watt meter, i test and it use 605w at the wall)
5 x 380 on a 1000w using 1100 at the wall ( now decrease power limit to keep under 1000)
now my 390 runs on a zalman 700w with an fx8300 oc and an 470 under clocked (using 690w) max 700w on 12V, i limited the power limit to keep under 700w at the wall
YOU MUST LIKE THE SMELL OF BURNING WIRES--
The optimal range of most PSU is 50-70 percent of the rated load. You are abusing your power supplies. --scryptr
AGREED! Unless you had one of those new fancy Seasonic PSUs that are prepared to go 100w overspec and still achieve an 80+ gold rating, and that would still not be optimal, for your current setup you should get at minimum an 850w PSU, and go with a more reputable brand than Zalman.
With an 850w you would still not be in the optimal range of a PSU, but at least it wouldnt be a fire hazard