The purpose of a voltage regulator circuit is to take a variable input voltage and produce a steady output voltage. Two common regulator types are linear and switch-mode. Linear regulators are simple, but waste a lot of power in the process of regulating the voltage. Linear regulators can be thought of as self adjusting series resistors.
http://www.solorb.com/elect/solarcirc/buckreg1/index.html
This Project describes a Protected 13.2V 40A Power Supply Unit which, provided the heat sinking and cooling fan are suitable, is capable of running at full power at 100 percent duty cycle.
http://www.qsl.net/vu2upx/Projects/40apsu.htm
This power supply is designed for general purpose use. Advantages of the circuit are first the voltage can be adjusted from 0V to greater and second it does not require a double sided secondary winding transformer.
http://www.circuit-projects.com/power-supply-circuits/general-purpose-power-supply-by-l146-or-ic-723.html
One of the main features of the regulated power supply circuit being presented is that though fixed-voltage regulator LM7805 is used in the circuit, its output voltage is variable.
http://www.electronic-circuits-diagrams.com/psimages/powersuppliesckt2.shtml
Nine voltage batteries are used in a wide variety of electronic devices. But, you often do not know when it is time to change the battery until the device stops operating.
http://www.discovercircuits.com/H-Corner/9v-batmon.htm
There are power supplies with greater current capacities on the same Digi-Key catalog page as those shown above. These should be avoided as they have a negative terminal that is connected to earth through the grounded, three prong plug. This could cause isolation problems between various parts of a layout and could cause short circuits or ground loops.
http://home.cogeco.ca/~rpaisley4/PSupply.html
This page presents various capacitor discharge power supply circuits for use with twin coil switch machine motors. Also shown are some optional wiring methods that can be used to enhance the availability and control of these supplies.
http://home.cogeco.ca/~rpaisley4/CDPSU.html
detect AC line currents of about 250 mA or more without making any electrical connections to the line
http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#aclatch.gif
well filtered variable 1.2-30 volts at 5 amps using LM338K
http://www.aaroncake.net/circuits/supply.htm
voltage regulator for 1.2V to 35V output voltages and up to 1A load
http://www.epanorama.net/documents/components/lm317.html