Magical energy sources

It's most likely a myth. Something people in Ogha used to wish for. Pray, in some cases.
It's unclear how the original description came to be, but plenty of the stories lead to a place that is already full of myths. Some explorers said that "a ghost revealed the design to them" in a time when any form of clean energy would have been welcomed by every possible civilization in Ogha. Others claimed to have stolen the original blueprints from the Black Smoke city itself.
Their attempts to actually build the machine or implement the technology in other ways were never successful, and the idea was completely abandoned after they developed other solutions.

Utility

The mechanism is supposed to extract energy from the magic itself. Some think it can be used by those unable to use magic, giving them an artificial ability to cast spells but that's not as attractive now that technology is widely known. Why would you go looking for an artifact that lets you use magic to achieve something, if you can use an easy to find artifact to achieve that thing directly?

What the known civilization doesn't know is that the blueprints are real, and they were, indeed, stolen from that hidden civilization, but not from the city itself (that incident was, actually, the reason why they interrupted communications with outsiders).
They didn't have all they needed to make it work (and they never developed those forms of technology, but there are several worlds had, even some Unaware ones like Earth and Exthod), but even if they had, that tech would have cause as much damage to the magic as combustion caused to nature.
The people in the city never put that version of the system to work, but they eventually designed one that was actually sustainable.
But remember, that's a secret that the Enlightened can't hear about ;)

— Escritora Novata