These modern, highly compact and lightweight USB-C power supplies offer the best ratio between clean power output and price on the market. One unit can power one Wii.
20W is easily enough for a Wii that's running Gamecube games and even most Wii games. Only with a Wii playing Wii games and with several accessories connected (Gamecube controllers with integrated LEDs, external hard-drive disks etc.) will the Wii draw more than 20W.
These power supplies also serve as regular USB-C chargers for smartphones or laptops, where intentionally charging them slowly can be helpful for long-term battery health. Especially convenient with this make is that each unit is just as big as a Euro socket, so on a multi-plug adapter, you can fit one of these in each Euro plug socket and make use of all the plug positions (which is not the case with most other USB-C power adapters).
For the double plug versions (USB-C + USB-A), keep in mind that if you connect a cable into the USB-A socket while a Wii is being powered with a USB-C to Wii power supply cable, the power supply will switch from 12V output mode to 5V output mode, which results in the Wii turning off.
Therefore, if you want to buy these power supplies for running video game tournaments, I advise sticking with the single-output version so that no competitor will accidentally shut down a tournament setup by plugging their charging cable into the second port.
For home / personal usage, however, the 30W dual-output version is usually the best choice.
AC power plug type: EU. 100-120V 60hz is however also supported, so these can also be used in Japan or North America; you just need to couple them with a passive US to EU AC plug adapter (and ideally, if intending to power several setups, a multi-plug socket such as this one).
