The Canon DSLR camera (right) needs continuous power during long exposure astrophotography, so a regular battery won't do. Above left is the AC/DC adapter that can be purchased separately, but many astro rigs are powered by a 12V battery power supply when in remote locations where AC power is not available. So, I built a 12VDC-to-8VDC converter, bottom left, using plans from here
. In order to be able to switch between the two, I terminated the cords in male/female plugs.