12V 10A aluminum shell switching power supply is used for centralized power supply of cameras. How many cameras can I connect at most? Does the line length matter?

You mean 12V power supply is used to power the camera from a distance? If the image is clear and stable when it is realistic, the power supply is not very reliable. Although it is very desirable from a safety point of view, all I come into contact with is that AC 220V is connected to the camera and then transferred to 12V DC for the machine.

Theoretically, if one camera works normally at 20W, the power supply of 12V 10A should be able to supply six cameras.

1000~ 1200m line length has little influence. If it is too long, it will be attenuated and the signal will be unstable.