The modelnumbers slightly differ for the ACD. The two letters behind the 4 digit product number are different. These two letters are:
1 for the external powersupply and for which voltage it is made
or
2 for the different type of powercord and the external powersupply is autoswitching
I don't know if it has a completely different powersupply, or that is is only the powercord. Here in Europe, the 23" has modelnumber 9178ZM, where the ZM is for Europe/220 volts. Other Apple products that have a build in powersupply and I know that they autoswitch to the correct voltage.