Most phone chargers (including Samsung, Apple and Nokia) are multi voltage supporting 100 - 240 V, 50/60 Hz.I have just been in Japan and for me it Worked ...
but still had some problems, I didn't actually use the 3DS in Japan except for the flight but I noticed with other things like the iPhone that it sometimes made problems after charging
as they only have 100V and 110V depending where you are as far as I know.
Some other people in the Hotel I have been reported about several problems with their phones and other things as well and I think it might be because of the different Voltage but not sure.