when You burn the HHO you get better combustion and it is cleaner. the engine runs better. the exhaust smells different. I don’t think you get more power as you imply
So the claim is changed from “extracting excess power from the alternator” to hydrogen acting as some sort of catalyst?
In the latter case, it should be possible to experiment with a hydrogen/hydrocarbon engine regardless of the source of hydrogen. (There gotta be cheaper, safer, simplier ways to get hydrogen.) I am *highly* skeptical that such alchemy has escaped notice for over a century of experience with the internal combustion engine.
If the former (”excess power from the alternator”) the claim reduces to a perpetual motion machine and can be dismissed out of hand.