Electric vehicles. Small diesel generator to charge??

It's more like 20hp to sustain freeway speeds which is like 15kW. Not unreasonable, but still a lot of charging power. Typical 220v EV charging stations charge at 6.6Kw, but DC fast chargers are 50kw. Up to over 100Kw for Tesla superschargers.

It could be done, but you'd need a decent sized genset.

For the record, the only true series hybrid car I know of was the Fisker Karma. It had a 2 liter turbocharged Ecotec that put out 260hp running a generator. Driveline was electric only.