PSU — Power Supply Unit
Converts wall power into clean, regulated DC for every component. Explore it in the interactive 3D viewer below, with the key facts about how it works and how it fits into a PC build.
By PC Anatomy contributors · Published 2026-08-11 · Updated 2026-11-12
What Is a PSU?
A PSU (Power Supply Unit) converts mains AC power from the wall into the stable, low-voltage DC power every internal component needs to run.
The Power Supply Unit takes mains AC power and converts it into stable, low-voltage DC for the system. Its quality determines not just wattage, but how safely and quietly your entire PC runs.
What Does a PSU Do?
The power supply takes wall AC and converts it into regulated DC voltages (12V, 5V, 3.3V), protects components with over-voltage, over-current, and short-circuit safeguards, and delivers clean, stable power during load spikes.
- Convert AC mains power to regulated DC voltages.
- Protect components with OVP, OCP, and short-circuit safeguards.
- Deliver clean, stable power during load transients.
- Power devices when the PC is asleep or off (standby rail).
How Does a PSU Work?
Inside the PSU, a rectifier converts AC to DC, a power stage switches it at high frequency, and transformers step it down to the 12V, 5V, and 3.3V rails the system uses. Voltage regulators and protection circuits smooth ripple and shut the unit down on faults. An 80 Plus certified unit wastes less energy as heat at typical loads.
Example Specifications
These values illustrate a common desktop setup. Specifications vary by model; check the manufacturer’s documentation before choosing or installing hardware.
| Wattage | 850 W |
|---|---|
| Efficiency | 80+ Gold |
| Modularity | Fully Modular |
| Rails | Single +12V |
| Form Factor | ATX |
Wattage
Wattage is the total power the PSU can deliver continuously. Add the CPU and GPU power draw plus about 20–30% headroom for transient spikes; 650 W covers most mid-range builds and 750–1000 W suits high-end GPUs.
Efficiency (80 Plus)
The 80 Plus rating measures efficiency at 20%, 50%, and 100% load. Gold (87–90%) and Platinum/Titanium units waste less heat, run quieter, and often use better internal components.
Power Connectors
The 24-pin ATX connector powers the motherboard, 4/8-pin EPS connectors feed the CPU, 6/8-pin PCIe connectors feed the GPU, and SATA/Molex connectors power drives and accessories. Modular units let you attach only the cables you need.
Safe Power Delivery
A good PSU keeps voltage within specification under load transients — critical when a GPU jumps from idle to full 3D load in milliseconds. Protection circuits (OVP, OCP, OPP, SCP) shut the unit down before damage can spread.
PSU in a PC Build
The PSU must supply enough wattage for the CPU and GPU plus headroom for transients, use the right cables for the motherboard (24-pin ATX, 8-pin EPS) and GPU (8-pin or 12VHPWR), and fit the case. A quality unit protects the whole build — a failing budget PSU can damage other parts.
A good PSU delivers consistent power under load spikes — critical when a GPU transitions from idle to full 3D load in milliseconds. Budget units fail under these transients and can take other parts with them.
Related Computer Components
Every part of a computer works together. Learn how the PSU connects with the rest of the system:
References and further reading
Frequently Asked Questions
What does a power supply do?
A power supply unit (PSU) converts the AC power from your wall outlet into the stable low-voltage DC power that the motherboard, CPU, GPU, and drives run on, and protects them from surges and faults.
How many watts does my power supply need?
Add your CPU's power draw and your GPU's power draw, then add about 20–30% headroom for transient spikes. 650 W covers most mid-range builds; high-end GPUs typically need 750–1000 W.
What is 80 Plus efficiency?
80 Plus is a certification for power supply efficiency. A Gold-rated unit delivers 87–90% of the power it draws, wasting less energy as heat than Bronze or unrated units.
Can a bad power supply damage my PC?
Yes. A failing or low-quality PSU can deliver unstable voltage that crashes systems and can take the motherboard, GPU, or drives with it. It is worth buying a reputable unit with enough wattage.
Explore the PSU in 3D
Use the interactive viewer to rotate, zoom, and inspect the PSU. Drag to orbit, scroll to zoom, and use the toolbar to reset the camera.
