By Rebecca O'Brien | Updated Mar 24, 2022
Understanding how to read an AC‑DC adapter is essential for matching power cords, selecting replacements, and ensuring safe device operation.
Locate the “output” label. The number followed by a “V” (e.g., 12 V) indicates the adapter’s voltage.
Right after the voltage, you’ll see a figure followed by “A” or “mA” (e.g., 3 A or 500 mA). This is the current rating.
Look for the diagram with three interconnected circles. The central circle has a gap on one side. If the gap faces the plus sign, the tip is positive; if it faces the minus sign, the tip is negative.
When possible, compare the adapter’s output specifications with the device it powers.
The “input” section tells you the wall‑outlet voltage required. A rating of 100–120 V matches standard U.S. mains; 200–240 V indicates a foreign voltage and may need a converter in the U.S.
mA means milliamps (500 mA = 0.5 A). Adapters with 100–240 V input work worldwide but may need a plug adapter. Bring your device when buying a replacement to ensure the correct tip.
Never guess polarity if the diagram is unclear. Contact the manufacturer for confirmation or a replacement. Using an adapter with the wrong wall voltage can damage the adapter and/or device.
