As the other user said, it's a separate power supply. The cable run to the camera from the DVR is usually a siamese cable with two halves. One for video and one for power. Either of these type of power supplies is normally used.

https://www.amazon.com/Monoprice-Channel-Camera-Power-Supply/dp/B0069MB6G0

https://www.amazon.com/VideoSecu-Security-Adapter-Channel-Connectors/dp/B002WM8ZV0