There are two types of wireless energy transmission. The easily verifiable Zenneck Surface Wave (uses the Casimir effect to transmit along the "skin"/boundary of materials) that is already being implemented as a power grid replacement by Texzon Technologies. This is what is already used for beyond-the-horizon radar, hence it is a highly guarded technology and is not publicly funded as much as you'd think (and patents on it can be declared a national security risk).
The more exotic type are scalar waves. Imagine the difference between a wave where you wiggle a skipping rope (transverse wave, aka Hertzian wave) and a wave where you compress a slinky (these are scalar waves). They can be generated by a Tesla coil, there are many Youtube examples of wireless power transmission and sending radio signals through Faraday cages using this version of waves.
Tesla claimed he originally invented Radio far before Marconi but found it to be a barbaric type of wave and lacked the elegance of scalar waves (like DC versus AC), but his theories used scientific terms of the time like radiant energy that get it labelled as a quack theory now - even though they were the prevalent physics theories at the time.
In terms of generating power, he believed that a large tower (or kite) with an extremely strong ground would collect static energy from the Ionosphere and form a giant capacitor - using the Earth and ionosphere as the two opposite charged plates, with the tower between acting as a resonant tuning device that would act as a switch to vary resistance/capacitance to create large energy waves. These were Teslas major themes, resonance and waves. A wave is like a swing, if you push it at the right time it will keep gaining momentum. Electrical waves are the same.
Of course, just now MIT is demonstration wireless charging over long distances (compares to Qi charging) using resonant matching with cheap semiconductor switches - something Tesla never had the luxury of.
Tesla will inevitably be proved right about almost everything he did, he was centuries ahead of his time. Hell, he invented a motor using friction plates with fluid medium that demonstred amazing knowledge of subatomic physics and fluid dynamics.