Power module, power supply
If you are going to be using the Apple in Europe, it may be as simple as
looking at the back of the unit or the power module/brick and determining
what the power label says and then buying a power cord for the country(s)
you are going to travel to in Europe. If it says 110-120 Vac 60 Hz and there
is a switch to be moved to 220-240 you have a switchable power supply and
will need to switch to 220-240 and buy a converter for the US power cord.
If it says 110-240 Vac 47-66 Hz then you have a switching supply and it will
sense and set the voltage accordingly. Power cords aren't cheap so buying
a set of international plug converters will save the cost of the cord and will
allow you to use the adapters for other electronic devices.
Hope this helps, and remember on returning to the US to reset the power
switch if in fact that is what needed to be set. Also most if not all big
computer manufaturers of late are providing supplies that auto range to the
voltage and will work world wide!