I've been looking at some induction heater builds on YouTube. These are fairly simple circuits, with a couple of MOSFETs and some caps. The output is fed to a coil, sometimes with a center tap, and any conductive substance placed inside the coil quickly becomes red hot. The circuit will typically run at 30 kHz, and I think this can be used for hho production.
These units are also available at Amazon, pre-assembled, and I picked up a 100W version for $13. It has two opposite phased outputs, and a center tap.
Anything useful I come up with playing around with this can be scaled up with my 1500W inductive cook top, which is equivalent to a couple of HP.