I have a US version Nintendo Wii and have to Use a stepdown converter which i must say is a tad annoying but today SuccessHK have released a 3rd Party Multi region AC Adapter for the Nintendo Wii at a price of $13.42
Heres the full details:
Product Features of Nintendo Wii Wii AC Adaptor
Input: AC100-240V
Output: DC12V 3.7A
Supports US, EU, JAP version Nintendo Wii