Where does tesla radiant energy come from?
Tesla Radiant Energy comes from the minds of people who want there to be something beyond Maxwell's equations, laws of thermodynamics and conservation of energy, all that boring stuff that stops wonderful things that they want to happen, happening. See also tin-foil-hat, and perpetual motion.

A Tesla coil emits ordinary electromagnetic radiation, but very inefficiently as it is not designed to be an antenna, so does not match the impedance of free space well at all.

It can also emit very pretty sparks!