Nyko Retro Controller Hub - 4 Port GameCube Controller Adapter for Nintendo Switch
From the manufacturer
Retro Controller Hub for Nintendo Switch
Get ready to use your classic GameCube controllers again with Nykos Retro Controller Hub for Nintendo Switch. The hub features 4-ports and allows for up to 4 GameCube controllers to be connected to the Switch for competitive and local multiplayer games. Retro Controller Hub plugs into the two USB ports on the side of the dock providing enough voltage to support up to 4 controllers.