How to Read an AC DC Adapter

Find the volts under Output

Knowing how to read an AC DC adapter is a skill that comes in handy during a variety of home projects. You can easily match power cords to devices by comparing voltage and polarity, and if an adapter is damaged you can use the information to find a replacement.

    Identify the voltage. Next to the word "output", you'll see a number with a "V" after it (such as 12V). This is your voltage.

    Find the amps under Output

    Identify the amperage. After the volts, there will be another number with "A" or "mA" after it (such as 3A or 500mA).

    This is an example of a

    Find the diagram that shows three circles connected by lines. The center circle will be open on one side. Whichever sign it opens to is the polarity of the tip. If the circle opens to the plus sign, it is tip positive. If it opens to the minus, sign it is tip negative.

    If possible, compare the information from the AC DC adapter to the device it powers.

    Find the voltage input.

    Check the Input section to determine the voltage it requires from the wall outlet. A rating between 100 and 120 volts denotes standard voltage used in the United States. A rating of 200 to 240 volts denotes voltage used in a foreign country, and the adapter will require a voltage converter to work in the United States.


    • An amperage listing of mA denotes milliamps. 500 milliamps are equivalent to 0.5 amps. AC DC adapters that have an input of 100V to 240V can be used with any voltage, but may require a country specific plug adapter. If you're going to purchase a replacement adapter, bring the device to the store with you so you can find the appropriate tip.


    • Do not guess about the polarity if the diagram is unclear. Contact the device manufacturer for more information or to order a replacement. Using an AC DC adapter with the incorrect wall voltage will result in damage to the adapter and/or device.

Related Articles

Ace Your Middle School Science Fair with These Science...
How to Calculate KVA from KW
How to Read an IC Part Number
How it Works: Voltage Relay
How to Calculate Millivolts to Amps
How to Calculate Three Phase Amps From Megawatts
How to Design an RC Snubber
How to Use a Variac
How to Calculate KVA to MVA
How to Get 12 Volts From a 48 Volt Golf Cart
How to Use a 9-Volt Battery to Power LEDs
How to Size a Transformer KVA
How to Measure Wattage With a Multimeter
How to Calculate Transformer VA Rating
How to Determine the Positive Side of an LED
How to Calculate Power Rating
How to Convert Watts into Kilowatt Hours
How to Measure Electric Motor Torque
How to Calculate the Duty Cycle of a Frequency
How to Size an Overcurrent Device for a Transformer