A. Check the voltage to the camera (under load) using a digital multi-meter, if below 10.8V then move the power supply closer to the camera.
B. For 12V DC cameras, only use regulated power supply rated above the current consumption, so that the camera is always receiving the correct supply which is rated above the current consumption.
C. Use thicker gauge copper cabling to reduce the voltage drop to the camera, using thicker cable will reduce the resistance between the camera and the power supply and therefore reduce the voltage dropped along the cable.