A GFI, Ground Fault Interrupt, outlet is used to decrease the chance of shock due to water. Most measure the flow of current between line and neutral. If there is a significant difference, the product assumes the current is flowing through ground-shock condition. It then opens the line. They do have to be checked periodically. Be sure the GFI you use is approved for your area.
Although ATM manufacturers don’t require a GFI outlet for an ATM, they do require that the outlet supplying power to the ATM be properly grounded (also referred to as an “Orange plug”).