Re: So it's plausible it can tell the difference between turned off and power out?
since I answered off the top of my head I thought I should check a few things
https://www.quora.com/How-do-I-find-the-electrical-resistance-between-the-two-leads-of-my-110-volt-wall-outlet-at-home
https://www.quora.com/How-do-I-find-the-electrical-resistance-between-the-two-leads-of-my-110-volt-wall-outlet-at-home
If you have a doubt about the wiring being faulty or something and hence you want to measure the resistance then.maybe a real electrical engineer can give a better answer. Alex? Others?
first COMPLETELY DISCONNECT ALL SOURCE SUPPLY AND FULLY ISOLATE THE ENTIRE HOUSE WIRING, BOTH LIVE AND NEUTRAL.
After that you could find the Resistance between any points in the dead wiring using a multimeter.
The resistance in this case between the two leads of the wall socket should be very high.
P.S. After the changed question details about resistance value of the source right up to generator / transformer.
YES you can find out out that resistance but for that you will have to ask the power supply company to shut down the power supply to the nearest transformer before your house then you may use a multimeter. You can not directly do it with the supply on. You can not go beyond the nearest transformer because beyond that the supply is isolated.