The alternator works no harder than the load imposed on it and can supply no energy until a greater load is imposed on it; the electrolysis device may impose a load of from 10 to 150 amps depending on design and volume of water being worked on.
This extra wattage must come from the engine working harder which burns more fuel; when the device is turned off the alternator goes back to the base load and does only that much work and the engine burns less fuel again.
At no time is there free work being spun off into the air.
Good explanation. Some people can’t understand that getting more power from an alternator requires using more power to turn it. No free lunch.
Prof....
I know. You don’t have to teach me about physics. LOL
Please.