Conversion Reactor
When Fayth Wilson activated the alien vessel on Tiger Mountain, one of the first things the ship's computer did was relay a message to her regarding the status of all major systems. One of the systems listed was the "Conversion Reactor." This may be the power source for the ship, but this has not been verified.
This technology has not been researched yet.
On a side note, when the alien ship was captured, the output of its reactor was very low. At one point, AJ Kamastafall went into the engineering space and attempted to locate a power supply. He found a removable device, perhaps some kind of fuel rod. It appeared "dirty" like a bar of white-hot metal with dark scabs of cooled material covering the majority of its surface. Despite appearing to radiate heat, it did not heat the air. In an ill-advised fit of curiosity, AJ briefly touched a fingertip to one of the glowing spots to see if it was indeed cool. He could give no answer, as contact with the material seemed to vaporize about a quarter inch of his fingertip. When he found a device used to clean the rod, the conversion reactor rating reported to Fayth by the ship's computer showed a greatly increased output.