one true way to prevent counterfeiters from circumventing your verification would be to give each plug a unique code, then have the device send off to your manufacturer servers to check the unique code is valid, which the device then remembers. you'd also have to either permanently lock the plug to one device, or have some pretty invasive location data to ensure the codes were genuinely unique though. either way it requires network connectivity, servers, etc
alternatively, you could have a long and complex call and response behaviour, perhaps dictated by a deterministic neural net. this would certainly be hard to counterfeit, but not impossible.
one true way to prevent counterfeiters from circumventing your verification would be to give each plug a unique code, then have the device send off to your manufacturer servers to check the unique code is valid, which the device then remembers. you'd also have to either permanently lock the plug to one device, or have some pretty invasive location data to ensure the codes were genuinely unique though. either way it requires network connectivity, servers, etc
alternatively, you could have a long and complex call and response behaviour, perhaps dictated by a deterministic neural net. this would certainly be hard to counterfeit, but not impossible.