Phind's Answer of Magic honestly wasn't far off, and the Ori, I think would appreciate it as they were a race so advanced that they wanted the inhabitants of their galaxy to worship them as Gods. Some of the only Ori tech explained in any degree was their genetic engineering of the Priors. Most of the Ship and weapon tech was so far advanced that it defies much of our current understanding of physics. Many of the feats we see them perform are clearly impossible to us. This was part of the Writer's intention, they spent the previous 6 or 7 years of the show detailing how Earth had become an interstellar species as a result of a war with a more advanced race (the Gou'ould). Over the years of the show they had stolen and reverse engineered much of their enemy's Technology.
The Introduction of the Ori was to intimidate the viewer, to show that for as advanced as the Humans had become, The Ori were so far ahead of them that they could barely understand how the technology worked much less how to counter it.
I don't remember hearing about the Ori ships being powered by Black holes per se, the only reference to black holes was regarding the "super gate" and that was explained as using the time dilation of the black hole to keep it open. The ships themselves looked like they were constructed around normal star gates and my wife and I often speculated that the gates were open to the center of stars, using the influx of energy to power the ships. How any of this works however was intentionally designed to be unexplainable.
In the end after all we were exploring a race that was millions of years old in the show.
