One of the most important things to remember about your cameras is their power polarity. Almost all 12V DC cameras are polarity sensitive, which simply means, if you connect the negative wire from your camera into the positive terminal of your power supply it will actually fry components in the camera. This will damage the camera and it is not covered under any manufacturer’s warranty.
24V AC cameras are non-polarity sensitive. There isn’t a plus and minus, you can connect them either way and you will be just fine.
There are also a few 12V DC cameras that are non-polarity sensitive but very, very few.
We recommend running every camera like it is polarity sensitive and labeling each and every cable so that simple mistakes are never made.