The PSU (Power Supply Unit) is the part that takes mains electricity from the wall and converts it into the low voltages your PC's components actually use. It's the gateway between the wall socket and everything else.
Why it matters
A PC that won't start at all — no lights, no fans, no beeps — is very often the PSU, the socket, or the cable. The PSU is the most common single point of failure for a "dead" machine.
What to look for when choosing one
- Wattage: the total power it can supply. A typical home PC needs 400–650 W; gaming or high-end builds 650–850 W. Slightly oversizing is fine and safer.
- Efficiency rating: 80 PLUS Bronze, Silver, Gold, Platinum. Higher = less wasted heat, lower electricity bills.
- Modularity: whether the cables are removable — tidier and better airflow.
Safety
A PSU holds a high-voltage charge in its capacitors even after it's unplugged. Never open one yourself — it can injure or kill. If you suspect it's failing, a technician can test and replace it safely.
If your PC is fully dead and the socket, cable, and power switch are all fine, the PSU is the first thing a technician will suspect.