I have no recent experience with power-assisted bicycles.
It's probably lack of need, as my area of measuring is quite flat, with very few hills. Thus I solve my lack of power by riding slower.
50 years ago Joan and I were in Bermuda, and we rented bikes with a small single-cylinder engine mounted over the front wheel. The driveshaft had a sandpaper-covered wheel which could be moved (with a lever) to contact the front wheel when an uphill was encountered, giving power assistance. I haven't seen one of these since. It was quite a simple rig and would be a boon to uphill riding.
Just did some surfing. My Bermuda bike was a VeloSoleX. See below.
VeloSoleX