That is a common misconception, japan uses 100V, where as U.S. uses 120V as confirmed by google and friends in the military stationed there. (not being a smartass)
Thanks for letting me know.
In Europe, there's a wide variety between 220V and 240V mains, but it doesn't really matter, since electric devices are made with these tolerances in mind for decades.
So it should be a similar situation as told by Necromancer.
And I agree with all those that say old style power supplies are wasteful even when the attached device is powered off.
I got a Goobay laptop style universal power supply for my Duo. It let's you select a variety of voltages using small jumper bricks, instead of the usual rotary switches. It also is able to supply enough current at the given voltage needed by the Duo, which is critical. Lots of cheaper popular universal supplies fail in that department.