Power supply is essential part in every electronic device. The whole system relies on it. If power supply fails – device dies too and there is a chance that sensitive parts may be damaged. Power supply solutions vary from device to device. They may work using different techniques depending on needs. Tim have described probably simplest power supply solution which converts Alternating Current (AC) to Direct Current (DC). Supply circuit consists of well known parts that are – transformer, which transforms voltage from 230V AC to 12VAC, them follows diode bridge rectifier, smoothing using large caps and regulation with standard 7805 voltage regulator.
Such solution proved itself in many designs. Its simple, cheap and builds fast. Tim put everything in short and informative post without overhead information. Following it you will be able to build 5V DC power supply in an hour.