What difference between 12v power supply and 24v power supply?

The working principle is the same, but the voltage level is different. 24v power supply is generally used in industrial control, while 12V power supply is generally used in monitoring systems.
Switching power supply is a power supply that uses modern power electronic technology to control the time ratio of switching on and off to maintain a stable output voltage. Switching power supply is generally composed of pulse width modulation (PWM) control IC and MOSFET.
Automation control commonly used AC 220V as a power supply. That is, the primary equipment power supply. Secondary power supply: DC24V is the power supply for lower-level equipment. Lower-level equipment is generally installed in the field or in the control cabinet, and the use of DC power mainly considers safety and reduces the complexity of lower-level equipment. Such as various transmitters, modules and isolators in DCS and PLC systems. DC 24V power supplies are also the standard power supply for international smart meters. DC 12V is rarely used except for some special equipment.

As an example of monitoring power supply, the camera is generally powered by 12V DC power adapter, the dome camera is generally powered by 24V AC, some cameras are directly powered by 220V AC, and some home network cameras are only powered by 5V. There are generally three power supply methods for the front-end camera in the project. 12V DC power supply near-end power supply The power supply can generally be placed in an outdoor protective cover or a separate power supply box within a range of 2 meters near the camera. If it is placed on the protective cover, the protective cover generally chooses a larger size, because the camera and the power supply will generate heat for a long time, and the larger space inside the cover is conducive to the overall heat dissipation.