If it has no switch of any kind on the outside it *may* be an auto-sensing unit (they aren't uncommon on newer components). Did a little looking on the on the 20SC itself and couldn't find any indication about whether or not it's meant to be a universal device (and Apple has pulled it off of their support website (apparently anything older than 7 years is "obsolete")).

If all the PSU does is output +5V/12V it shouldn't be hard to replace - an ATX PSU shouldn't have issues providing that (and you might even be able to find a dual voltage stand-alone PSU that can do that too). Alternately, if in doubt, use your step-down transformer.

Thanks obobskivich, yes I think I agree with you to be on the safe side im going to use my step down transformer.

As far I know these are two different ranges.
100-240V - mostly called as "full range" but somewhere as "wide range" voltage imput;
100-140V/220-240V - mostly called as "wide range" voltage imput, this one exist with manual switch and autoswitch.
Most Apple items are 100-240V. My 20SC chassis also 100-240V, I'm using with 230V (actually 242V that I have measured), although it is European version (assembled in Ireland). So if it's PSU is works well, it must support the 240V source.

Thanks for that Gona, but I think for my own peace of mind I'm going to use it with the 110V step down transformer.

manic232 wrote:

Does this mean that I can just plug it into a 240V supply and it will automatically switch?

If the primary voltage is expressed like that, then it doesn't need to "switch" as such.

In most switchmode power supplies the voltage on the primary side isn't important, because after the AC is rectified it goes into a self-regulating switchmode circuit. The availability of current is more important than the AC voltage in these setups.