Most small RF and network devices such as cameras, switches, and access points run on small Direct Current (DC) power, as low as 5 Volts to as high as 24 volts. To feed power to such devices from the mains which depending on the region can range between 100 Volts AC and 250 Volts AC, an AC/DC power supply is needed.

AC/DC power supplies step down the AC 110 voltage to the required DC low-voltage level and converts it from alternating current to direct current. Stepping down the voltage can be done using a transformer, but with modern switching mode power supplies, inductors and semiconductor devices efficiently do the job. Conversion from AC to DC is done by a diode rectifier. Rectified current is filtered through one or two passes to refine its waveform.

The final stage in the power supply output is precautionary: a voltage regulator may be added to ensure correct output voltage at all time, a reverse polarity protection circuit may be included to protect both the output device and the power supply from reverse polarity and short connection.

Common power supplies for RF and network devices are rated at 12V, 18V and 24 V. 5 Volt devices are usually fed by USB power adapters. AC input cables vary from fixed to removable power cables. The DC output is commonly terminated to a male DC Barrel connector jack.

The DC barrel connector is a cylindrical connector with a variety of sizes. The most popular standard is 5.5mm X 2.1 mm, known as Type A. A variety of the Type A connector feature a screw-lock mechanism for more secure connection.

Adapters for compatibility between different sizes and orientation are available. The outer contact of the connector is the negative terminal while the central contact inside the barrel is positive. The DC barrel connector is used in several DC power applications including switches, routers, and laptops.