@Liam
you need a Power and Phase inverter, from 220v 50-60HZ to 110v, this will lump out a lot of heat by the way. check the phase (in hertz Hz) on the American PSU.
I would recommend getting a new UK 220v from AmigaKit or even eBay if you are lucky, although the latter, you not sure how long its gonna work for and doesn't come with a guarantee where the one from AmigaKit does i believe