This power supply does not really excel in power efficiency, but it is the cheapest and most compact solution for a small power supply.Note that the low voltage output is directly connected to the mains; it can not be used when the low voltage part can be touched (e.g. chargers).With the component values of this circuit, the circuit can supply 12V /15mA max
Source: http://www.geocities.com/tjacodesign/supply/supply.html