2. A power supply is a device that supplies electrical energy to one or more electric load. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (e.g., mechanical, chemical, solar) to electrical energy. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source.

3. Battery:A battery is an alternative to a line-operated power supply DC power supply:An AC powered unregulated power supply usually uses a transformer to convert the voltage from the wall outlet (mains) to a different, nowadays usually lower, voltage. AC power supply:An AC power supply typically takes the voltage from a wall outlet and lowers it to the desired voltage Switched-mode power supply:A switched-mode power supply (SMPS) works on a different principle. AC input, usually at mains voltage, is rectified without the use of a mains transformer, to obtain a DC voltage

4. A modern computer power supply is a switch with on and off supply designed to convert 110- 240 V AC power from the mains supply, to several output both positive (and historically negative) DC voltages in the range + 12V,- 12V,+5V,+5VBs and +3.3V. The first generation of computers power supplies were linear devices, but as cost became a driving factor, and weight became important, switched mode supplies are almost universal.

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