There are several ways to distinguish the positive and negative poles of a power adapter:

　　Judging by appearance identification

　　-Most power adapters will clearly indicate the positive and negative poles. Common symbols include "+" for positive pole and "-" for negative pole; Or use the English words' Positive 'and' Negative 'to indicate. These labels are usually printed near the interface of the adapter or in a prominent position on the housing.

　　-For some adapters that use special interfaces, the shape design of the interface may reflect the difference between positive and negative poles. For example, one side of the interface may have a protrusion or groove, and the corresponding device interface may have a corresponding depression or protrusion. This design can ensure correct polarity connection.

　　Measuring with tools

　　-A multimeter is the most commonly used tool. Turn the range switch of the multimeter to the DC voltage range (usually select the appropriate range, such as 20V), and then contact the red and black probes of the multimeter with the two electrodes of the adapter output terminal. If the voltage value displayed on the multimeter is positive, then the red probe is in contact with the positive pole and the black probe is in contact with the negative pole; If it is displayed as a negative value, the polarity of the red black probe contact is opposite.

　　-Light emitting diodes (LEDs) can also be used to determine polarity. Generally speaking, the long leg of an LED is the positive pole, and the short leg is the negative pole. Connect the LED in series with a current limiting resistor (e.g. 100-500 ohms) and then connect it to the output terminal of the power adapter. If the LED emits light, then the positive pole of the power adapter is connected to the LED long leg; If it does not emit light, it may be due to reversed polarity or no output voltage from the power adapter.

　　Judging based on circuit connection habits

　　In some common electronic devices, there are usually certain circuit connection rules. For example, in a DC powered circuit, the red wire is usually connected to the positive pole, and the black wire is usually connected to the negative pole. If the output line of the power adapter has color differentiation, you can refer to this rule to preliminarily determine the positive and negative poles. However, this method is not absolute and still needs to be based on the markings or measurement results on the adapter.

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