Yea of course you can run a 10kW generator off HHO. But it can't create enough gas to run the engine driving it. It can't even create enough gas to compensate for the power it took from the engine.

I once saw somebody on the news who'd made such a thing from a plastic bottle and a pipe. He plugged it into his car's alternator and fed the gas into the air intake. The silly reporters took it seriously, but that was 2 years ago and I never heard any more about it.