I have one of these "small" electric breaker hammers.
15 Amp, 120 Volt Breaker Hammer
I've tamped quite a few wood posts with it. I usually run it at less than full speed because it will overheat with all of the damping I get from the soil. Plus it's no fun when my tamping head heads for China alongside the post.
With my 2-1/2" tamper end on it, it will turn any medium rock into gravel in a few seconds. I think with a homemade adapter it would make a great T-post driver. It runs good on my 5000w generator. There are bigger electric breakers but you don't want that much machine on top of your post. I envision slipping the breaker with adapter over the post before setting the post upright. After the post is in, the height will be down to where you can lift it off. Maybe a handle right on the driving adapter would help with removal. I just about have myself talked into making an adapter this week. Do you want to see a demo?