It doesn't violate physics. Just traditionally the technology to do this is cost prohibitive. For example, a fuel cell which does this normally costs $100,000 - $1,000,000 bucks. Why? Because the catalysts are things like platinum and palladium and the required surface areas are large. Worse, they frequently require frequent servicing. Those that don't are why the costs span such a large range.

If you spend $1,000,000 to create "cheap" H20 from distilled water, is it really cheap?

Now, watching this video, I can assure you the guy is an idiot. You cannot get more energy out than you're putting in. This is a physics fact. He's simply using up his alternator to place a higher load on his engine to generate HHO. If he's claiming a higher return then he is claiming over unity. Which violates physics.

This technology cannot provide more energy than you get out. The energy required (at least using this technology) to crack the water will ALWAYS require loss. For example, his alternator is not 100% efficient. This is his energy source to crack the water. Cracking the water requires more energy than you can get out. This is two losses right there.

I know someone that tried this with a "commercial" device that was supposed to crack water into hydrogen. It ended up destroying his engine.

He was a lucky little shit because his father worked at the Honda plant in Marysville and had a line on an engine from a car that had been in a transport wreck. The car was fine but written off, so it was parted out to dealers as "used." Brand new engine for nothing, the guys at the factory shop did the replacement.