Tesla was a certified genius who went certifiable, not totally unlike Howard Hughes in his final years, though with considerably less money.

Tesla had a good high-class European technical education, and came to America to work for Thomas Alva Edison, a 'self-educated' genius with a contempt for formal training. ("If I want a mathematician, I can hire one" attributed to him). Edison also made the biggest technical gaffe of his career in backing to the hilt electrical transmission via Direct Current (DC) via his Edison Electric Co. Tesla knew this was a poor choice due to the problems inherent in transmitting DC electric power over any distance. He left Edison and went to work for a business and industry visionary, George Westinghouse. Their AC system won out as it was destined to do, and along the way to the electrification of the modern world, Tesla was the fount of many Westinghouse patents, including advancement in induction motors and I believe the three-phase system that is used throughout modern industry worldwide. One of his earliest projects was the generation of power by harnessing most of the flow of water that heads for Niagara Falls. Edison's company had to switch to AC power which caused Edison to remove his name from a company that continued operation as General Electric.

Tesla pursued other projects which he didn't bring to fruition, among them the transmission of electric energy at high enough frequencies so as to need no wires (Sort of like drawing power from your radio antenna, hugely wasteful unless the power can be 'beamed'. This Tesla did not accomplish.

I'm writing this via memory, so forgive any omissions. Tesla separated from Westinghouse at some point, I don't know why, but as he grew older he lived a solitary life and felt underappreciated for his great contributions to the power industry, although he wasn't ignored, he never received the popular adulation such as a man like Edison. He developed some notions that may have been obsessive compulsive, and these contributed to his estrangement from other folk, and possibly his death, although he lived to a ripe old age.

Tesla left some notebooks, and brief autobiographical writings. Considering his importance, the literature on him is quite sparse. This has left an opening for a lot of utter nonsense to be promulgated which makes rather free with his name, mainly the kind of entertaining rubbish that gets bandied about on late night AM talk radio in the States. Beware.

As for 'over-unity' energy devices, it's a fancy way of saying it puts out more energy than is put into it, in other words, it's a 'perpetual motion' device. A distinction must be made to allow for the fact that when you burn a log, you are putting in the energy of a match and getting out many thousands of times that energy from the combustion of the log. But what you are really doing is 'harvesting' the stored energy of the fuel that is the wood. It's the same whether that energy is stored in paper, gasoline, or the food you consume. Perpetual motion comes from the notion that you can truly create energy from nothing by utilizing some principle of mechanics or electricity that no one has figured out before. When it comes to electric motors, that business with motors made of magnets lends itself to con-artists and idiots because it's pretty easy to mis-measure what's going in and what's coming out, not to mention, hide a battery in the middle of the contraption.

A good rule of thumb is that any time someone brags about over-unity, you should button up your wallet, because they're looking for 'investors', A K A suckers.