On 2016-01-21, John Heath wrote:
On Thursday, January 21, 2016 at 12:13:52 AM UTC-5, 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

Think of voltage as pressure.

.... and as you gradually ease into thinking of voltage as pressure,
relax and concentrate on supressing that strange feeling that makes you
want the schematic for a "regulated power supply", even though you don't
know WTF that means.