Electricity demand issue

I had a similar issue before and managed to fix it, Unfortunately I don’t remember the exact step-by-step process.
One thing I noticed is that buildings complaining about power don’t have the yellow power line connecting them from the street. You can check under Service Power mode.

What I tried was:
- Move one of the complaining buildings to a clear area so it’s easier to see the connections.
- Temporarily demolish one power plant (the cheapest one you have).
- Place the cheapest power source (like a Wind Power Plant) from the Menu right next to the affected building and upgrade it a few times.

The idea is to “refresh” the service flow and see if the yellow connection line appears between the power source and the building. Try moving the building around to see if it picks up the service, once it works the whole city starts receiving it and the population rises again.

Try fixing one service at a time (power first, then water, etc.).

If that doesn’t work, bad luck, I don't know :(  but at least this method only costs a small amount.

You have just received the new 2.0 update welcome to the club of other such players. Majority of which have alread quit the game altogether. If you decide to continue playing then be ready for a new adventure of stress and frustration while attempting to progress your city, be prepared for it to become nigh on impossible to play without being forced to spend real money. Be prepared to find it a chore instead of the fun playing game it once was