The first method: We can use a multimeter to measure the resistance of 2 wires. The 2 wires with high resistance value are connected to 220V, and the low resistance value is connected to 12V.
In addition, most of these voltages have one set of terminals on the power supply side, and several sets of 36V24V12V outgoing lines on the low voltage side. After the power supply can be connected, use a multimeter to measure the low-voltage side, and the voltage is displayed as the 12V terminal connection.
The second method: use a multimeter to pass a lower resistance value, such as Rx1 or Rx10. The ones that are connected in two are a group, and then the resistance value is measured. The group with the larger resistance value is the input terminal, which is connected to 220V. If you can see the windings of the transformer, the end with the thinner wire diameter can be connected to the input.

220v to 12v transformer 500W-Sanyuan Electric
The third method: The 220V to 12V transformer is generally the red line input and the black line output, but there will be differences between different manufacturers. For details, you can ask the merchant. You can also look at the label on the transformer. The label will specify the input voltage of the transformer, the color of the input lead, and the output voltage and color of the output lead.
The 220v to 12v transformer is a conventional type, and we often use it. If you know how to wire it, it will be much more convenient. The most effective way is to ask the merchant directly. If we have any special customization, we can also find the merchant to customize.