QUOTE(Poiteen @ Jun 15 2008, 04:14 AM)

But guys, by power supply you guys mean the whole unit - right?
It's fairly possible that although the OP's computer doesn't have a switch, it can be used with 110. if they look at the info supplied with the computer, or around the back of the computer, it's quite common to find the input AC as 100-240v or 110-220 or similar. In that instance the OP only needs a new plug or a plug adaptor, no?
No, the power supply is a smallish box of wires, fans, transformers, and such within the computer case.
As for using the 220V computer with 110.... Would you want to try it with YOUR computer? I wouldn't. $40 for a power supply sounds like cheap peace of mind to me.
However, even if the voltage range allows for it, you need to check the Hz rating. UK and USA are different. I would think that a power supply would only work within a certain Hz range (unless there was a switch allowing you to activate a different set of resistors, diodes, and such inside the power supply.)