Bizarre question I know, but I’ve noticed via Dolphin that I’m able to do tech better via an Xbox One pad vs the Gamecube pad for Smash games and have been curious about this for over a year. I haven’t run into an adapter that goes to this extreme yet, but I’d honestly be willing to pay whatever necessary to achieve this.
As far as I know, there are very few (if any at all) converters that allow a newer peripheral to be used on an older platform, and I don’t believe any mass-retail converter does anything USB to GameCube. You’re looking at adapting a controller to a system 2 generations back…
Since very few of the custom arcade PCBs handle full analogs, your best bet is probably something along the lines of creatively gutting the XBO controller and mapping the buttons and analog sticks directly 1-to-1 to a GCN padhack of sorts…
Way I see this working, the OP needs someone to make them a custom board. An Xbox One to Game Cube controller adapter is possible, you just can’t do it with with whats available from retail.
A custom made DIY solution is needed.