All AC adapters are labeled with their voltage and polarity ratings. This information is important because it allows you to make sure you use the correct AC adapter for an electronic device. The voltage and polarity output of the AC adapter must match the voltage and polarity input of the device. If an AC adapter is lost or damaged, knowing how to read AC adapters will enable you to pick out an appropriate replacement.

AC adpaters have specific ratings which must match their accompanying devices.

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Find the input rating of the AC adapter by looking on the AC adapter for the word "Input," followed by the letters "AC" and a number followed by a V. This tells you how many volts the adapter draws from the power source.

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Determine if you need a voltage adapter. The standard AC adapter input in the United States is 100 to 120 volts. If the input voltage listed is higher, you will need a voltage adapter to use the AC adapter in the United States. If the input voltage is in the 100-120 volts range, you will need a voltage adapter to use the AC adapter in other countries where the standard input is 200 to 400 volts.

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Look at the voltage output of the AC adapter. Below the input, look for the word "Output." This line tells you how many volts the AC adapter transmits to the device. For example, "Output: 12V."

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Check the amperage output. To the right of the voltage output will be another number, followed by either "A" or "mA." For example, "4.62A." A stands for amps and mA stands for milliamps. There are 1000 milliamps in 1 amp.

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Look for the polarity of the AC adapter. Polarity is identified by a icon with 3 circles connected by a straight line. The left and right circles have either a plus or minus side inside them. The middle circle will be open facing either left or right. If the middle circle opens toward the plus sign, the polarity is positive. If it opens toward the minus sign, the polarity is negative.

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Check the device to see if the AC adapter is a match. The output voltage and polarity much match the input ratings of the device.