The black hole tap is an Ori designed power source, most famously used to power their supergates. This technology is extremely advanced, given the difficulties in actually reaching the surface of a gravity sphere of that magnitude.
In a black hole, the gravity of the body is sufficient enough to retain all energy emitted as opposed to a star that expels such energy as radiation. The energy produced in a black hole can’t achieve escape velocities and is instead contained inside the event horizon. This means that all the luminous energy of 10 stars expelled over thousands, if not millions of years is pooled beneath the event horizon just waiting to be tapped.
The first trick is getting a tap in place without it being crushed into oblivion. The Ori designed multiple shield layers augmented with massive inertial dampeners all powered by the energy the tap absorbs from the environment…so as long as the tap has sufficient power to reach the surface it will forever be able to sustain itself once in place.
The second trick is getting the power back out. The Ori used a micro-wormhole the size of a human’s finger to transmit the processed energy to the nearby supergate. Whenever the supergate’s capacitors ran low or an outgoing wormhole needed to be established the micro-wormhole would connect first and supply all the power the supergate would need in real time for as long a time as necessary.