What peripherals are you using with the pc? I just built several ITX pc's that do not have a dvd or cd, and uses a SSD Hard drive. This kept the current down low and we were able to use 60W 12 volt power supply bricks that run on 120vac. I plan to incorporate my design of a 12 vdc UPS into the system. This would be more efficient than the standard UPS that needs to convert from 120vac. Just because you have a 200W power supply it does not mean the pc will use that much power, it will only take what it needs.
However if space and power are not an issue, then a standard 250W ATX power supply will do nicely, and probably cheaper.