Given the chance of things going awry by trying to do a heavy assault at the plant, I’d find ways to interrupt the lines at a distance. Perhaps “interrupt” is a better wording than “take out”.
Now, if those control boxes can be taken control of (not “taken out”) by a light assault, that’s a different matter. Which I noted. Tanks are not a “light assault”, in my book.
I have very little understanding of how a power plant reacts to the sudden stop of electrical usage.
I also have little understanding of how to assault a powerplant to get control of it. But I would certainly want to clear out resistance in the area, starting with any buildings (hideouts) potentially used by the opposing force, that are not integral to the plant operation.
Cutting the wires doesn’t remove the hidden opposition.