Please note, this is only if you play on a PC as it works using console commands!
A collection of mods and ends.
www.nexusmods.com
This is a mod that checks the settlement you're currently in for power grid errors. This is something that exists in the vanilla game. SS1 would trigger it when you deleted a plot and the power pole deleted with it, which is why in SS2 you need to delete the power poles by themselves. Also, the wireless glitch will cause errors along with other ways of powering a settlement without wires. Not every time, but it can happen.
With this mod installed, you open the console and type cpg (check power grid). It will tell you how many grids exist and either "no errors" or there are x grids with errors. If errors exist, type cpg 1 and it will remove all the the bad nodes. You then need to rewire the settlement.
This leads to one other thing that confused me at first; the fusion generator said it was producing 100 power, but connecting to it did not power the grid. I finally realised that you need to scrap the generators and replace them. After that mod fixes the errors, generators still show they produce power, but they don't.
I was having horrible problems with CTD in and around settlements because I saw a video about how to use the wireless glitch, which makes it easy to power things in places the wires won't reach. After using this tool and rewiring everything, the problem disappeared. The mod that XxA1xX mentioned, Place Everywhere
https://www.nexusmods.com/fallout4/mods/9424 solves some of the problems I solved with wireless glitching. Place allows you to run wires through walls, trees etc. So rather than using a conduit pass through to get the power outside to the inside, I attach a wire to a wall or ceiling conduit, pick it up, walk inside and put it in place. Role playing? We drilled a small hole in the wall and pushed the wire through it.
Good luck!