Basically speaking,? 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 right replacement one, especially the laptop ac adapters. As we all know that different brand laptops have different model number and part number, if we could have a better knowledge of the ac adapters, we could easily find exactly what we need.
First of all, 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). Generally speaking, for selecting the right replacement one, the Amps may be higher but they cannot by lower. For example, If the wattage requirement for your laptop is lower than the 60W or 90W output of the adapter, it will not damage your laptop, your laptop will only take the amount of power it requires. If your laptop needs 45W, then either the 60W or 90W will work OK. If your laptop needs 80W then you will need the 90W one as the 75W one will not be powerful enough.
This is an example of a "tip positive" diagram.
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.
Secondly, find the volts under Output
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.
Then, remember to 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.