7809 is a 9V Voltage Regulator that restricts the voltage output to 9V and draws 9V regulated power supply. The 7809 is the most common, as its regulated 9-volt supply provides a convenient power source for most TTL components.
7809 is a series of 78XX voltage regulators (as known as L78xx, LM78xx, MC78xx...), the xx is replaced with two digits, indicating the output voltage (for example, the 7805 has a 5-volt output, while the 7812 produces 12 volts).
Linear regulator like 7809 has performance issues with respect to battery life and Power loss. If you are looking for an alternative for 7809 with better efficiency and less power loss, then we would recommend a DC Buck Switching voltage regulator.
Buck converters may be preferred over 78xx regulators because they are more efficient and do not require heat sinks, but they are more expensive.