This question is probably easy, but as a total electrican noob I couldn't really find a suitable answer so far.
Some circuits, like amplifiers, require a -12V and a +12V rail respect to the ground. Given that I have only one 0-12V supply that is reasonably powerful, the simple question is:
What would be the simplest way to get that -12V out of the supply, with a reasonable (say 500mA, more=better) current?
The things I already know: the -12V - 0V - 12V is alike the 0 - 12V - 24V setup. (But what if I need to connect this circuit's ground to another? What if I have a common ground with the supply? Then I do need -12V.) I also have a basic understanding of amplifiers, transistors etc.