DCC Boosters take the DCC signal generated by the DCC Command Station and electrical power generated by the Power Supply (also called Transformer) and combine them to provide the power with the encoded digital packet signal to operate the trains. You might need a booster if you have expanded your layout, or are building a larger one, and are planning to run more locomotives at one time. You will need a power supply for each booster but only one command station.
Command Centers are a complete unit and may be used to replace or upgrade the command center that came with your system.
Since the advent of digital sound decoders, another type of booster that boosts the programming signals, to better program sound decoders, is often advantageous.