The MEG is the first way Tesla devised to produce alternating current. He understood that rapidly switching and pulsing electricity let him utilize positive and negative polarity and engage more current. He figured out a simple, common sense circuit to produce AC in the 1880s.
It takes a little current for the first pulse to bring the MEG from inactive to active, to be sure. Then, the pulse is stepped up by an output coil, the majority becoming current and the rest close looped back to the other core to fire the next pulse. Thus, the source charge problem is solved, and you're making electricity without moving parts or fuel.
Think of the MEG core as like a transformer core divided in two. Each side has an input coil and a larger output coil. Here's a schematic of the circuit which is true to Tesla's version, at least so far as I can determine. In that this is one of the best kept secrets of anything our government ever stole, it's hard to be absolutely sure.
There are tricks to this, and Tesla said if it isn't correctly engineered and configured, it doesn't work, like anything electrical. But, as you can see from the schematic, there's not much to it. Are we really that close to energy self-sufficiency? Yes indeed.
From the circuit's patent and the experiment's replication one sees the importance of the core's metallurgy and of proper exploitation of the magnetic "flux transfer principle" as described by R.J. Radus in the July, 1963
Tesla went on to design the rotary generator and everything in the grid, and the hydroelectric generation and transmission facility, not because they were better. They weren't. They were based on truncated mathematics, and render less than one percent of the electromagnetic energy present. But, they were what made money for the people who employed him.
Many wonderful stories are told about Tesla's dealing with manufacturers, the military and utility companies. He was seen by some as a threat to the established order, so he and his work were buried in history. The system we use today is his. He insisted the generator-grid system isn't sustainable, and it isn't.
Overunity is clean, sustainable power without cost. Taking the energy cost out of home, office, manufacturing, transportation and agriculture changes the economic weather dramatically and launches a million new technologies. Some suggest in time it could produce such abundance no one would ever lack for a vocation, and the monetary sytem itself would become obsolete. That's a very big story.
Consider Tesla attempted to sell his unmanned aerial vehicle to the military at a bargain price. They probably didn't understand it, and built today's air corp instead. The vehicle used no fuel and was operated by remote control. Since that time, we haven't needed ships, trains, planes, cars, trucks, bridges or roads. The year? 1915.
The only reason the government pushes wind and solar grid plug-ins is to perpetuate existing energy industries, because wind and solar won't make 20% market penetration in 50 years, and probably many more. Electricty will become more expensive, and we'll get a world full of increasingly costly natural gas cars and trucks. That doesn't curb CO2 emission, and if you've ever seen a natural gas explosion, you should not want that.
A better world is possible, but not if we don't design it. And how can we design it if we don't know what a better world is? Supression of this technology is a crime, and every president since 1943, when Tesla's notes were stolen, has deserved removal from office and prosecution for failing to declassify and disclose it.