Electronic equipment requires a stable DC voltage in order for ICs and transistors to operate properly.
There are two primary methods for obtaining this DC voltage: using an AC‑to‑DC power supply that converts commercial AC mains, or using a DC‑to‑DC converter that converts a DC power source such as a battery.
Each of these types is available in isolated and non‑isolated configurations, depending on whether the input (primary) and output (secondary) circuits are electrically isolated.
Currently, constant‑voltage power supplies are broadly categorized into switching power supplies and series‑regulated (dropper/linear) power supplies, with switching power supplies being the mainstream choice.
Switching power supplies offer advantages such as high efficiency and low weight. However, because the rectified voltage is converted to high‑frequency AC and then back to DC, they tend to generate more noise.
Series‑regulated power supplies have the advantage of low ripple and low noise, but they are larger and heavier.
To maximize system performance, it is essential to understand the characteristics of these power‑supply types and use them appropriately.

Table 1.1 Compares some of the features of Switched-mode Power Supplies with Linear Regulators