Had the opposite problem about a year back- We had a bit of a brownout around 6PM in the winter, and when things came back they came back REAL bright. In the studio all my racks shut down to 'Extreme Voltage' and in the shop the power meter that feeds my bench was showing 145VAC (Canada, nearish our drop transformer, so I'd normally see 117VAC on a hot summer day, or 123VAC in the winter.)
It didn't rectify itself after a few minutes, so i ran around shutting down anything that wasn't a switch mode, and called our municipal hydro co. They came out, came to the door, and I told them the issue and what preceded it and said I wondered if likely they'd got a damaged primary winding, since the leg to leg was nearly 300VAC, and evenly balanced on the secondary side. They thought that sounded like a solid theory- did some checks of their own to confirm what I was saying, and that it affected the other 4 or 6 houses fed from that transformer. Came back to the door about 20 minutes later and said yup, that's what it was, and they'd be sending a crew out to replace it within the hour. Sure enough the trucks rolled in about 60 minutes later, shut down power for 45 minutes and did their thing. Linemen and Linewomen don't get nearly the credit they deserve, esp the ones who do the emergency and troubleshooting calls. The crew that came to my call asked me if I was in the industry, and I explained that I wasn't, but adjacent, on much smaller scales, and that it was mostly because of my shop and studio setups and metering that I noticed right away the scope of the problem. I figured most people would barely notice their lights being a bit brighter until things started to pop. Apparently I was right- I was the only person who'd called in the issue (that ultimately persisted for 2 hours or more by the time they came back to replace.)
One Canadian lineman/troubleman has a fairly popular YouTube channel where he does everything from showing splicing techniques, and explaining the equipment, to just doing his regular day-to-day work. One thing he makes a point of saying a lot is that a lot of times people assume that hydro co's know when a fault happens- and that's surely true when it's major or causes a notable disturbance on the grid that the main dispatch can see- but more often then not they don't know about faults that are more limited in scope. And that if you have a problem, you're always better to call it in. The more data they get the faster and better they can work. Any information you can give them about preceding events, noises, whatever... it all helps save them time.
He actually said one of the big problems can be that in less-dense suburban and rural areas you can get a squirrel pop a transformer or switch- but because of nature being what nature is, often times an animal or bird will run off with the Char-broiled Squirrel Combo before they can get there, and they can spend hours trying to find a fault that doesn't exist because they couldn't confirm a "Fur Fault"...
So ok that whole long ass JR-style TMI is basically to say - Call the utility and let them know. That's way out of spec and it's probable that you're the only one who knows about it. They're probably happier on the whole to know about it BEFORE it causes damage to either your equipment or theirs. That shorted winding in my hood might have held on for a bit- but i'd bet if no one had noticed, the next big sign would have been a transformer vault fire, under a tree, overhanging my neighbours house...
