Power Supplies - External/Internal (Off-Board)

Power supplies are devices which swap one type of electrical energy to another. While most computers have internal power supplies, many electronic devices use external ones. For example, some monitors and external hard drives have power supplies that reside outside the main unit. These power supplies are connected directly to the cable that plugs into the wall. What is external power? External power supplies are devices that convert ac power from a wall outlet into lower voltage dc or ac power to be used directly by electronic circuits. External power supplies are used to power a variety of electronic devices, including: laptop computers, printers, cordless phones, cell phones, etc. What is an internal power supply? A power supply unit (or PSU) converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use switched-mode power supplies.