That power supply only puts out 1200mA, which is 1.2A. It won't work at all because the computer is going to draw a lot more than 1.2A. The HDD power thing that provides 3A is better, but still nowhere near enough.
You need something that's going to ut out 15A @ 12v at the very least, preferrably 20A or more.
I use an ATX power supply I have lying around and it powers my setup in the house with no problems.