What device is used to convert power from AC to DC?

A rectifier is the correct answer because it is the specific device designed to convert alternating current (AC) into direct current (DC). This conversion is essential in various applications, such as providing power to electronic devices that require a steady and unidirectional flow of current.

Rectifiers achieve this conversion by allowing current to flow through in only one direction, effectively filtering out the negative part of the AC waveform. This process creates a pulsating DC output that can be further smoothed using additional components like capacitors, depending on the application's requirements.

Understanding the function of a rectifier is crucial, especially in electrical and electronic systems, where most devices need a stable power source. Other devices mentioned in the options serve different purposes: a circuit breaker is used for overcurrent protection, a transformer changes AC voltage levels but does not convert AC to DC, and an inverter performs the opposite function by converting DC back to AC.