In the field of electronics, VDC stands for volts of direct current. Direct current is the type of current that comes from a battery or the power supplies of many electronic devices.
Direct current flows at a constant rate in a constant direction. It is usually directed through conductors, such as wires. Direct current provides a stable voltage for sensitive electronics, such as computers. These devices would not function properly on the variable voltage of alternating current. The power grid in most parts of the world is alternating current. This requires the power supplies of sensitive electronics to have a rectifying circuit that converts the alternating current to direct current. The voltage and polarity of alternating current takes the form of a sine wave. In the United States, the electrical grid alternates at a frequency of 60 hertz.
Desktop PC power supplies provide 3.3, 5, and 12 volts of direct current to supply different parts of the system. Power supplies for laptops and other small electronics are marked with their output in volts of direct current on the bottom or back side of the unit. Batteries are marked with their output in volts of direct current on the side of each battery. It's important to ensure correct polarity when powering direct current devices. Incorrect polarity can ruin the device.