Well, I don't understand all the physics behind it, but apparently the device uses the naturally occurring energy found in rare earth magnets via magnetism to power the device. And it's a well known fact that there's a humongous amount of energy tied up in atoms and molecules, as is evidenced by the atom bomb. There was also something that came up, an at that time undiscovered principle of magnetism that allowed energy to both be extracted from the interacting of magnetic fields.

Again, I don't know or understand it all, but there was some pretty interesting physics behind it. I don't know how much further they ever went with the design, or how much actual energy could efficiently be extracted from the process, but the initial designs didn't render a whole lot of surplus energy.