Unstable Power R290X

[miner765]

What may be the cause of such jumps in voltage/power? Running TWO 290x on ASRock H81 BTC mobo. Using 2 molex connected to MB, the mobo also says no not use powered risers.

Again, if someone actually helps me out - I'm willing to give bounties in LTC.

(2400W is more then enough power for them, planning to get 6 on)