I also have one of these. The power is plugged into the back of the blue VGA plug (the one that plugs into your computer).
If you look at the back of the blue plug, you should see a hole.
You need a standard 12V, 3A power supply with positive in the middle, and negative on the outside. These are cheaply available from an electronics store, such a Maplin, or online via eBay or Amazon
Stefan C., February 2012