This has been an interesting topic, and provides good info for new RVers to Mexico. With all due respect to Chris, we found that the electrical pedestals and the wiring in the RV parks we stayed at were C**P, and we learned to adapt. After getting a tingle off the RV because of a reversed polarity outlet I bought testing equipment (circuit tester, clamp meter etc) and a power conditioner to cope. Even the (then) new RV park in Celestino with new plastic electrical boxes, 30 amp service and USA quality breakers gave our surge guard fits as the voltage dropped in and our of range, I suspect it was caused by the incoming supply or the main transformer as we were one of the very few RV's in the park at that time. I generally wouldn't consider working on a pedestal down there as you never know how it was wired.
I learned to cope and live off the power that was available, even sharing a 30 amp service with 2 other RV's because of the quality location on the ocean and great RV friends. I was able to live off about 5 amps in that park.
Mexwanderer, I'm wondering why the parks don't meter and charge for electricity just like is done in the US? That would eliminate the gouging and perhaps reduce the overall electricity usage, I've seen some pedestals with small readouts that don't require the purchase of those large household meters.