This power supply is a linear type, it is completely isolated from the AC line, so can be run without being grounded. The power comes in on a IEC (Euro) cord, and is fused with a panel mounted fuse holder.
http://www.andrewkilpatrick.org/mind/bench_supply/
It uses 12V 5A transformer and some basic components to give put unregulated +12V. One resistor is used to reduce the current for the LED light.
http://www.ee.washington.edu/circuit_archive/circuits/Supply.GIF
This is a simple regulated power supply that can give adjustable voltage from 3 volts to 18 volts. The current capacity is 10 amperes. This circuit is overcurrent protected. This circuit can be modified for higher current ratings if needed.
http://www.anatekcorp.com/ttg/tiptrick.htm#10 amp Power Supply
This circuit provides 0-30 volts, at 1 amp, maximum, using a discrete transistor regulator with op-amp feedback to control the output voltage. This power supply has constant current mode suitable for charging batteries.
http://members.tripod.com/michaelgellis/power2.html
This is a simple circuit which can provide an adjustable voltage source of 0 to 330 Volt. The supply is short-ciruit proof. the current is limited to about 100mA.
http://www.geocities.com/tjacodesign/300vsup/300vsup.html
This is a high quality power supply with a continuously variable stabilised output adjustable at any value between 0 and 30VDC.
http://www.electronics-lab.com/projects/power/003/index.html
It inputs AC100 V and it is possible to take out 12 V of the two DCs which are independent as the output.
http://www.hobby-elec.org/e_ckt19.htm
To work the circuit which used the operational amplifier and so on, the positive and the negative power supply become necessary.
http://www.interq.or.jp/japan/se-inoue/e_ckt19.htm
AC100 V 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 4 A.
http://www.hobby-elec.org/e_regu.htm
simple circuit based on 78xx fixed voltage regulator IC, those ICs are available for some fixed voltages between 5 and 24V
http://home.maine.rr.com/randylinscott/nov98.htm