The Nintendo GameCube Controller Adapter now works on Nintendo Switch and is compatible with Switch games, thanks to a secret feature in the recently-dispatched 4.0 system update. It works with all of the Switch games released to date, including Pokkén Tournament DX. Does this mean that GameCube Virtual Console could be on the way? Or maybe Super Smash Bros. for Nintendo Switch?! Only time will tell; in the meantime, you can check out the video below for a demonstration on how the Wii U USB controller adapter works:
Super Smash Bros. GameCube Adapter now compatible with Nintendo Switch
Pokémon Blog 