ktmrfs,
And I continue to spend my life in the power delivery industry. Our bible is ANSI (American National Standards Institute) C84.1 when it comes to voltage. It spells out two ranges A and B, with A being the range to meet the majority of the time. Each range includes service voltage (what we care about) plus utilization voltage (at the receptacle.) None of this works out to 10%, but can be approximated by 5 at the service. If your electronics meet a wider range, that's good. Maybe an excursion into range B won't kill them.
I see you are in Portland. Perhaps you've heard of PGE.
https://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltage_tolerance.pdfThe NEMA standard is +/- 10, but starts at 115 nameplate instead of the 120 nominal used by ANSI.