Take a look at your Wii U AC adapter - on the bottom, it should say the supported input voltages. On mine, since I purchased it, and live, in Australia, it says 230V-240V 50Hz. This will be different for different regions of the world.
For example, this one:
It supports 100V up to 240V at 50Hz or 60Hz - this one is basically universal. If yours is like this than the only thing you might need is a physical plug adapter so it will fit in your power socket.
You can check here to find your country's mains power voltage and frequency. Make sure your AC adapter voltage matches your country's! Otherwise it is most likely not going to work and would be dangerous to use.
If your country's mains voltage is not compatible with the AC adapter, there are converters available which (provided you get the correct one) will convert, say, 110V, to, say, 230V. But for the cost of those it might be best in that case to simply buy another Wii U AC adapter that is compatible for your country.