Computer power supply units (PSUs) provides all the voltages the computer needs to function. Most computers use the ATX form factor, a standard that describes which voltages and connectors a PSU should have to be compatible with other hardware.
The ATX standard has three main voltages (3.3V, 5V, and 12V), and two, almost never used, negative voltages (-5V and -12V). Recently, I was thinking about how I could make a computer power supply that accepted a 12VDC input, while still providing the range of voltages needed. Indeed, regulating 12V down to 5V and 3.3V is not so difficult, but obtaining negative voltages along side these positive ones was a challenge for my mind.
Looking online I found that almost all examples of dual polarity power supplies involved the use of a center tapped transformer and AC voltages. This was not the most practical method if my input were to be a DC source. So, rather than begin complicating the idea, why not find out if these negative voltages are even needed at all.