The Retro Receiver is a Bluetooth dongle; it enables 8Bitdo-, PS3-, PS4-, Wii Remote and Wii U Pro-Controllers to connect to an original NES!
It fits beautifully into the original NES controller ports, supports multiplayer games (two receivers and controllers needed)
No additional AC Adaptor needed: It gets the needed power directly from the controller port.
Finally, it's possible to use wireless controllers on your NES.
Additionally, it can also be used as a bluetooth dongle on a PC.