A power supply is a device that provides electrical power to equipment. It converts power from a source into the voltage and current the device needs. Your computer has one. So does your phone charger, your TV, and your router. Without it, the device gets no power.

Power supplies can be linear or switching. Linear supplies are simple and quiet but inefficient. Switching supplies are more complex but smaller and more efficient. Most modern electronics use switching supplies. They convert AC from the wall into DC for the device.

Key specs

• Wattage: total power it can deliver
• Voltage: output voltage, like 12V or 5V
• Current: maximum amps per rail
• Efficiency: how much power is wasted as heat
• Form factor: ATX, SFX, external brick

Power supplies fail. Capacitors age. Fans clog. When a power supply dies, the device goes dark. In data centers, redundant power supplies keep servers running if one fails. Power is the silent prerequisite for everything electronic.