Why is the socket voltage in Mexico 127V?
Saw this on another site  https://www.electronicspoint.com/threads/127-volt-standard-voltage.164594/


  Much, maybe all, of Mexico supplies single phase power via 2 phases from
  three phase power. In the US that is known in the power industry as
  "network power" and is usually 120/208 volts. Now 208 volts sucks. But
  to get 240 volts from such a configuration, you'd have to have 138.5 volts
  on line to neutral, and that is a bit too much for most things that want
  120 volts. In Mexico they have chosen a compromise where the L-N voltage
  is just a little high (127 volts) and the L-L voltage is just a little low
  (220 volts).


Sounds reasonable. Haven't been able to find any search terms that yield anything better.