I don't think it works like that. The only known way to make antimatter is to convert energy into matter-antimatter pairs, so basically you need the same 100% of energy to produce antimatter in the first place. (In fact, I think the current physical theory prohibits any kind of matter-antimatter conversion, but I'm not a physicist so I might be wrong.)
So, if we had enough energy to make these antimatter, we could simply use the energy directly, without going through the massively inefficient step of funneling that energy into liquid helium and superconducting magnets and city-wide vacuum circles and so on.
I think OP might have been thinking of s/efficient/dense
Antimatter is certainly the densest way we know to store energy, which is great when it works. But unfortunately, it's also the densest way we know to store energy. Which is not so great when it explodes.
Technically, all forms of energy "production" we have are basically extraction from an existing store of said energy. Try reading[0], it's about the two guys who proposed a black hole powered space ship. What they suggest is extraction energy from the sun (an existing source) and making a black hole (or maybe more from the same one), and then use that to power your ship.
"With a set of four machines: black hole generator, black hole drive, power plant, and a self perpetuating black hole powered black hole generator, the potential is enormous. "
So, if we had enough energy to make these antimatter, we could simply use the energy directly, without going through the massively inefficient step of funneling that energy into liquid helium and superconducting magnets and city-wide vacuum circles and so on.