Switched Mode Power Supply (SMPS): The switched mode power supply acting as a DC to DC converter first rectifies an AC input voltage (240Volts), converts it to DC and, chops this DC in a “chopper” and converts it to a higher or lower level of DC (5 to 12 V DC Volts). Typical modern applications include computer power supply and the power supplies in TV and Video sets. The wattage of SMPS is around 150 to 500 watts.
SMPSs are three types :

1. AT SMPS
2. ATX SMPS
3. BTXSMPS

1. AT SMPS :
AT stands for Advanced Technology. These are all old SMPSs. They had 12pin power connector, this is called as AT power connector. They were used in Pentium-I, Pentium-MMX, Pentium-II and Pentium-III CPUs.

2. ATX SMPS :
ATX stands for Advanced Technology extended. They had 20pin Power connector, this is called as ATX power connector. They were used in Pentium-III, Pentium- IV and AMD CPUs.

3. BTX SMPS :
BTX stands for Balanced Technology extended. They have 24pin Power connector, this is also called as ATX power connector. It has 15pin SATA power connectors. They are used in Dual core, core2duo, Quad core, i3, i5, i7 and latest AMD CPUs.