On Wednesday, January 20, 2016 at 9:13:52 PM UTC-8, wrote:
l wish to know the difference between negative 48 volts and the normal 48 volts.
Also l will be glad if a could have a circuit for a regulated -ve 48 volts power supply at 3A. thanks

Thanks a lot Jeff you've actually given me a good understanding. so I can build a normal 48 volts supply and ground the positive terminal instead.