Adjustable Turning

How do I make an electrical circuit that cuts off electricity below a certain level?

I am trying to put together a circuit that will cut electricity off completely when demand falls below a preset or adjustable level and then turn the power back on full when demand for full power is required again.

There is a hole in your logic.
If you cut power completely, the attached devices will have no power. If there is no power, they can’t turn on and demand more power!!! (unless, they have a backup battery or secondary Power Source).