This is a continuation of this question. Suppose we have a grid which distributes say one gigawatt total power and all this power is perfectly fully consumed by electrical devices.
However all consumer devices are regulated - each either has a switch-mode power supply or it's powered through a switch-mode voltage stabilizer. So it can be a good old perfectly resistive tea kettle but it would be powered via a high-power switch-mode voltage stabilizer which tries its best to output exactly 230 volts (I'm using European mains voltage here).
Suppose at some point of time a small fraction of consumers disconnect their devices from the grid. So now generation exceeds consumption and grid voltage rises a bit. However consumer devices are regulated and they refuse to drain more power. Those fully resistive tea kettles are connected via switch-mode voltage stabilizers which will not pass the higher voltage through.
Where will excess power go?