He did assert that he could transmit a LOT of electrical energy wirelessly, and he convinced some well-heeled investors to finance him for some time while he developed that idea. But it never panned out -- not even close -- and I'm not aware of any trained physicist or electrical engineer who believes that Tesla's approach is possible today. High power wireless transmission of electrical energy requires close magnetic coupling or very high frequency (microwave) and directional antennas. Dangerous to anybody who gets in the way of the beam, and difficult to convert back to a more useable form - - say, to power an electric motor.
In his later days he was a weirdo and a con man. I don't know of any documentation that supports the notion that Tesla was "done in" by the establishment because he and his ideas posed a credible threat to their electrical monopoly and profits.
Here's the electrochemical whiz kid demonstrating a few different means of wirelessly transmitting power. At 11:33 he explicitly refutes the notion that Tesla could have gotten free electrical energy from the air.
No + and - designation on the input power terminals of a device that is AC powered, such as that bulb. In an Alternating Current (AC) circuit the current flow reverses every cycle. So half the time the current is flowing into one terminal and out the other, and half the time out one and into the other. No + and -; both terminals get a ~.
BTW, I have the exact same model multimeter as Whiz Kid -- a Fluke 87 V. (Imagine discovering that Nikolai Lugansky plays the same model Bechstein 212 that you practice on at home.)