The 78xx family is commonly used in electronic circuits requiring a regulated power supply due to their ease-of-use and low cost.
[1] 78xx ICs have three terminals and are commonly found in the TO-220 form factor, although they are also available in TO-92, TO-3 'through hole' and SOT-23 surface-mount packages.
These devices support an input voltage anywhere from around 2.5 volts over the intended output voltage up to a maximum of 35 to 40 volts depending on the model, and typically provide 1 or 1.5 amperes of current (though smaller or larger packages may have a lower or higher current rating).
The 7805 is the most common, as its regulated 5-volt supply provides a convenient power source for most TTL components.
The 7803SR from Datel is a full switching power supply module (designed as a drop-in replacement for 78xx chips), and not a linear regulator like the 78xx ICs.