There are so many amazing energy inventions. The problem is they almost always require professional manufacturing which can't be done at home. So I prefer the simplest ones.
As has been shown here, about the Walter Russell coil generator, mankind moved away from the original correct design by Faraday. He had the correct perpendicular arrangements in his motor. Tesla followed Faraday's principles with his Unipolar Dynamo. And he made improvements. With it's very high current and low voltage, it was used for welding. That can be modified now, by rectifiers and a Cockcroft-Walton voltage multiplier, to get a house current. Voltage is also increased by using multiple disks separated by insulation layers. I'm not certain of this, but from something I think I heard in my father's business truck shop, when I was less than 10 years old, it's possible that those Unipolar welders continued to turn by themselves after they were started.
Here's how it would work. Tesla's Notes covered cutting the copper disk, between the electromagnets, into curved, spiral sections. The spiral curved paths, on the Unipolar Dynamo, are like a large electromagnet coil winding. They force the current, that runs through the disk, to produce a magnetic field. Curving the spirals in the right direction would reinforce the electromagnetic field acting on the disk. The stronger the current, the stronger the magnetic field would become, which increases the output.
My idea, to modernize it, is to use two neo cylinder magnets in parallel, one above the other, on two separate axes. The two magnets are arranged in opposite polarity. A carbon fiber belt, or other conducting belt, would wrap around the outside of both magnets to be the electric connection. The disk part would become a very heavy gauge pancake coil, attached to both ends of each magnet.
It may or may not be self-running. It doesn't matter if it's less than unity. Faraday's correct arrangement would make it far more efficient than modern generators that fight themselves.