Review on Optimized GameCube Controller Adapter for Wii U, PC, and Switch - NEXiLUX by Rodney Gonzalez

Works with Switch. My 4th port doesn't respond properly, but I usually only use the first two, so it's ok. I doubt the problems are common, maybe just the wiring is loose. GC controllers don't come with all the switch buttons, so you can't play some games with just controllers. But when paired with a customization joystick, it works great for Mario Karts.