Maybe this will help
The Problem is power so ithis can help you
Apple M8661LL/B DVI to ADC Display Adapter you can find it in ebay or other stores I had the same problem so i swiched from my imac to PC. It felt a little awkward. But because i couldnt fully utilize my gamepad Logitech g13 which I needed for my e- sport i had to make that move.