When should a Linear Power Supply be used?

Linear power supplies are designed for low noise and are often considered quiet since there is no high-frequency switching. They are used anywhere that excellent regulation and/or low ripple is required, as well as needing low electromagnetic emissions and excellent transient response. (Transient Response is the way the circuit responds to energies stored such as in capacitors and inductors. If a capacitor has energy stored within it then that energy can be dissipated or absorbed by a resistor.)

A linear power supply typically uses a large transformer to drop voltage from an AC line to a much lower AC voltage and then uses a series of rectifier circuitry and filtering processes to produce very clean DC voltage. 

Linear Power Supply - Advantages / Disadvantages

• Large & Heavy
• Efficiency around 30-40%
• Simple Design
• Low EMI Noise
• High Cost (Due to Material)
• Can only step down an input voltage to produce a lower output voltage.

The disadvantages of linear power supplies are that they are heavy, large, and have lower efficiency as compared to switching power supplies. 

You may also refer to the following Power Management video for additional overview information about power.