Electricity — México
México's electrical grid is 127 volts AC, 60 Hz, while the US and Canada are 120 volts AC, 60 Hz. All three countries use the same North America type A (non-ground two pins) and type B (grounded three pins) plugs and sockets. The voltage differential between México and US-Canada is negligible, so appliances should work interchangeably between countries. If traveling with 3-pin appliances, make sure to bring a 3-pin to 2-pin adapter.
Travelers from other countries should buy a universal converter/adapter that adjusts the voltage and adapts to different plug and socket configurations. They're widely available in travel stores for between US$10-40, depending on the number of different socket configurations supported. If your home country does not run on 120 volts make sure the adapter adjusts the voltage as well. For a list of voltage and socket requirements by country, read the awkwardly named Wikipedia article "Mains power around the world."