This is the simplest version of a transformer less power supply to power low current devices. It can give 30 to 40 milli ampere current and 12 to 15 volt DC depending on the input voltage.
CX is the most important part of the circuit to drop high volt AC to low volt AC through Capacitive reactance property. Bleeder resistor R1 discharge the stored current from the capacitor when the circuit is unplugged from AC outlet. This prevents shock hazard since the capacitor stores more than 400 volts for many days. The low volt AC is rectified by the full wave diode bridge and made ripple free by C1. So the output gives minimum 12 volt DC @ 30 mA current which can be used to drive 6 LEDs in series.
Caution: There is no galvanic isolation between the power supply and the gadget. So not use this circuit to power costly equipments. If strong spike develops in the AC lines, it may destroy the power supply circuit.
The circuit board is at mains lethal potential. So take adequate safety measures during operation. Enclose the circuit is a shock proof case. Do not try to test or trouble shoot when the circuit is connected to mains. If you are not experienced in handling high voltages, do not construct this circuit to avoid shock hazards.
Circuit in PDF