Wynona Inspectapedia is not a good site for a diy'r to go to. There is a lot of misinformation on that site.
Really!? Seriously, I thought I'd made a great "find" when I stumbled across it.
It has some good information, and I do mean some. But not a site to be taken literal. I am a regular on diychatroom.com. There are regulars in there that are in the trades. I myself have been around electricity and electronics all of my life. My father was a Radio Man in the Air Force and a ESS-4 tech for the telephone company. You can pretty much state that technology and knowing how to read a schematic, along with programming is in his kids blood.
The only time we really reference Inspectipedia, is for the Panel info on the old Fed-Pac panels.
What the OP is doing, is how we would troubleshoot circuits in a home when I have to do work in my own home, or for someone else. We have also done that on board ship, when we would be within 50' of the junction box and needed to tone out a circuit.
As for the OP. Using an extension cord is what most of us sparky's will ask someone to do, to try and figure out if it is a panel issue, or a single branch circuit issue.
The problem with most older homes, is that they are all tied in on the same branch circuit. Kitchen's, Pantry's, Dining rooms can also be on the same circuit for the baseboard and lighting.
Now if you get into the really old homes that had only four, maybe six circuits. You really have to know how to troubleshoot in those setups.
I always look at the voltage at the outlet first, to see what I am getting. Then go to some other circuit that I know should be on another let, and take a measurement. If they are not correct, then I go to the panel and start checking at each individual circuit breaker or fuse, to see what the voltages are. Same with the two legs coming into the house.
If I find one leg out of whack, then I will monitor it for about a week or two and see what happens. If still out of whack, the Power company is getting a call to come to the house to pull the meter and check voltages.
The OP really needs to turn off the power to the various branch circuits, and pull light switches and outlets and check for "Backstabbing" along with incorrect grounds.
You would be surprised at what kind of fun workmanship is found in homes & even mobile/manufactured homes, after multiple people have lived in the structure.
It does not take long for bad connections to cause electronics to go bad. That is why I am a firm believer in using a whole house surge protection, along with a secondary layer of surge protection. Either a UPS with Surge protection, or a surge strip.
I went as far in my place, and placed both our furnace and power-vent water heater on a surge outlet. Especially since they both have electronics in them and they cost more then I make in a month, if I had to replace them, due to a power surge.
