Mexico's electricity system is the same as that of the USA: 120 V; 60 Hz. Any electrical equipment you carry with you that operates at the higher (240v) rate will need to be dual-voltage (e.g. hair driers). A lot of electrical equipment (like video cameras, digital cameras, laptops) that operate on 12 volts via a product-specific adaptor will happily cope with dual voltage - check the adaptor and the device instructions to be sure.

You may need a socket adaptor. Most plugs in Mexico are the same as in the US; two flat prongs. Some have a third, circular prong for earth, and adapters can be sought for these too if the plug you want to connect to doesn't have the third (earth) prong socket.