Triple-monitor Flickering

Hello, i recently decided to upgrade my setup by adding two extra ASUS VE228HR 21.5" monitors on top of my ASUS VG278HE 144hz 27" (i use them in PLP).

(I run GTX-660 Dual-SLI and i use a Corsair CX750M PSU.)

When trying to use all three monitors in SLI (All connected to the same GPU 2 with DVI and one with HDMI) my main-monitor starts flickering when set to 144hz and the lower i set the hz to the less frequent the flickering gets.

I have a hunch that it is because my GPU doesn't get enough power but i really have no idea.

Help would be much appreciated and keep up the good work :)