A subspace power generator was a device used by the Cardassians to distribute energy to other technological devices with the involvement of subspace.
In 2374, such a generator was installed on an asteroid-moon in the Chin'toka system. It was used to send power to the various orbital weapon platform in the star system.
During the First Battle of Chin'toka, Chief Miles O'Brien detected the generator, and the USS Defiant was able to imprint the generator with a Federation warp signature. Thus fooled into believing it was an enemy target, the weapon platforms fired on the generator, destroying it. (DS9: "Tears of the Prophets")