This power supply circuit module is a compact, easy to build. It uses negative variable power supply module. This power module is ideal for powering any application requiring a DC supply at current levels up to 1.5A.
Diodes D1-4 form a bridge rectifier which converts the AC input voltage into a DC level. They also allow [...]

This simple circuit, consisting of two LEDs and a photo diode, generates a negative voltage with a current level of a couple milliamps. It is ideal for supplying a negative rail to low power “rail to rail” op amp circuits [...]
Source: http://www.discovercircuits.com/DJ-Circuits/negsupply2.htm

Sometimes you need a simple negative power supply. The best example is the contrast PSU for common small LCD device. Building -5V from a battery or a wallmart supply isn’t really easy.Here is a simple circuit that is able to provide -5V, -12V, -15V. The circuit used the MAX 764/765/766 series. You can simply change [...]