Nikola Tesla produced an aerial device which draws power via an insulated metal plate. The larger the plate and higher the elevation, the greater the energy accumulation.
T. Henry Moray produced an apparatus that was capable of putting out 50 kW of usable power without any apparent power input. This type of power is called 'cold electricity' and was demonstrated and repeated many times.
The materials describing this type of energy are scarce but you can find them on this website. (See: Radiant Energy, Pulsed Power, Aerial Systems, Resonance, Electromagnetic, Superconductors).