What power supply provides a current that flows in one direction only?

Direct current (DC) is defined as an electric current that flows consistently in one direction. This characteristic is fundamental to DC, making it suitable for devices such as batteries, electronic circuits, and certain types of power supplies where a stable and unidirectional flow of electricity is required.

In contrast, alternating current (AC) fluctuates and changes direction periodically, which is not applicable when focusing on current that flows only in one direction. Wireless power supply refers to methods that transfer energy without physical connectors, and transformative current is not a standard term in electrical engineering. Thus, understanding the nature of DC as a unidirectional flow clarifies why it is the correct answer.