Electrical current comes in two main forms: alternating current (AC) and direct current (DC).
Alternating current (AC) changes direction periodically. It is the type of electricity supplied by wall outlets.
Direct current (DC) flows in one direction. Batteries and many electronic devices use DC power.
Most medical devices require DC power, so AC from wall outlets must be converted using rectifiers and power supplies.
A patient monitor plugs into AC power but uses internal circuits that operate on DC.