Blackholes don't provide extra power to a Stargate and here is why.

[SciTrek]

Okay first of all, Hey, this is Matt from SciTrek and I think I have figured out the science behind why a black hole seems to power a gate almost indefinitely. From the outside, it very much appears to be the case that a blackhole will generate enough power to make the Stargate remain open past the 38-minute timeframe, but I think we have been looking at it all wrong, and it's more an effect of time dilation than it is power consumption.

So we know the effects of a black hole make it so from an outside perspective time is slowed down to a crawl. seconds on the side of a Blackhole will in fact be many days/weeks from the perspective of onlookers.

That being said, I always thought it was stupid that a blackhole could somehow "power" an active Stargate. I mean, black holes are literally condensed points in space that suck in all matter, they are not a power source.

What I think is actually happening here is (I'm going to include some logic that hasn't been confirmed in the show here) The stargates as we know, have a subspace connection, they communicate with each other. The 38-minute timeframe must be a two-way communication. Let's use the example of Earth dialing the planet with a black hole.

As we know time was slowed down for the team on the side of the black hole, whilst it was several weeks/months for Earth and went way past the 38-minute timeframe, the gate on the other side only experienced a few seconds at most. Therefore my theory is there is some sort of exchange, where Gate 1 says to Gate 2 - Okay I've been open for 38 minutes. Gate 2 responds with, "No I've only been open for a few seconds" and therefore the time limit is increased to accommodate the gate with the time dilation.

With this theory, it means, that the gates would naturally shut down by themselves given enough time, but as we know the closer you get to a black hole the stronger the effects of the time dilation. Meaning that the gate would probably be open for billions if not trillions of years until the communication is received from both gates that 38 minutes had passed on both sides.

TLDR: Blackholes don't power stargates, It's just time dilation.

I'd love to know your thoughts on this.

[Xaeden]

They doubled down on the idea that a black hole can supply energy to the gate during the Ori arc.

The Ori's followers used artificially created micro black holes to power the Supergate, and Earth dialed a Milky Way gate from Pegasus by placing a Stargate in proximity of a Pegasus black hole. Earth then triggered an energy spike so the outgoing wormhole would jump from the Milky Way gate to the Supergate, which prevented the Ori from using the Supergate until Earth terminated the connection 11 episodes later.

That's important not because of the length of time that the connection remained active, but because it's well established that Stargates need a stronger power source to dial between galaxies than Earth is able to manufacture. Thus, there would be no way for them to have been able to block the Supergate from the Pegasus galaxy if Stargates don't get an energy boost when near a black hole's event horizon.

[StargateMillennium]

Yeah, as Xaeden mentioned, they have established black holes can provide power. But the idea of powering something using a blackhole isn't unheard of. There are several theories out there so far.

One is called the BZ process and it is to take advantage of the rotational energy effectively turning it into the galaxies biggest wind turbine.

There is using the ergosphere which is essentially a belt around the blackhole where if matter flies down it, half of it will begin getting pulled to the event horizon while the other is launched into space with even more energy than it went in with.

The acretion disk also produces energy and it's been theorized you could build a pseudo Dyson-sphere (a Dyson ring if you would) just around the acretion disk to harvest that energy.

[Rohan]

One is called the BZ process and it is to take advantage of the rotational energy effectively turning it into the galaxies biggest wind turbine.

Or a perpetual motion engine.

Also to note that the stargate built by the Ancients are composed of naquadah which are a room stable super conducting element which is so good at absorbing energy about anything could be a power source.

Seeing as black holes draws in all matter including light itself, not too much of a stretch where a stargate is absorbing the extra power from what a black hole is pulling in and concentrating within the accretion disk.