We don't currently have an official adapter available for the Nintendo Switch. However, Nintendo recently released firmware update 4.0 that enables GameCube controllers to work on the Switch when used with their official GameCube-Wii U adapter (we can't yet confirm if it works with 3rd-party ones like this, but expect it should). Some of our customers have confirmed that our 5in1 adapter (GameCube connection) will allow the X-Arcade controllers to work on the switch with that official Nintendo adapter. To enable it, press L & R simultaneously when pairing controllers and use the analog/dpad modifier to get the joystick to work.
We cannot confirm whether 3rd-party GC-Wii U adapters work also, but if you own one and can test it please do let us know.
We can also confirm that this Brook GameCube-Switch adapter does NOT work with our adapters.