nrf24 based wireless adapter for SNES controllers. Should also work with NES.
Ironically, you'll need an extension cable. Cut it in half so you can connect the controller side and console side.
Worked with both my real SNES and my Retron5. I'm not a good enough player to tell if there is lag.
More information here: https://hackaday.io/project/12940-wireless-snes-with-nrf24