AC 100 Volt is used for the input of the power unit. The output voltage can be changed from 5 V to 30 V. The output current can pour a maximum of 4A
http://www.hobby-elec.org/e_regu.htm
This basic and versatile 5V supply uses a zener diode and an emitter-follower transistor.
http://www.edn.com/article/CA92007.html
An electronic circuit that strives to keep both the size and cost of a line powered DC supply small. The circuit transfers power from the 120vac line to a voltage regulator circuit by discharging a capacitor through a small high frequency transformer, twice each power line cycle.
http://www.imagineeringezine.com/e-zine/off-line.html
http://www.anatekcorp.com/ttg/tiptrick.htm
Einfach Schaltungen für QRP
http://www.qrp4u.de/docs/en/powersupply/