Power supply: wattage, connectors and why headroom matters
The component people economise on, and the one failure that can take others with it.
Safety level: informational · Time: about 12 minutes · Level: intermediate
The power supply is the part it is least sensible to save money on, because it is the only component whose failure can damage the others.
Applies to
Desktop PCs, new builds and graphics-card upgrades.
Sizing it
Add up what the parts draw, then leave real headroom.
The graphics card dominates: its rated draw is usually most of the total. The processor is next. Everything else — drives, fans, memory, board — is small by comparison.
Headroom is not padding. Modern graphics cards draw far more than their rated figure for very short bursts — milliseconds, but enough that a supply sized to the average will trip its protection and shut the machine off. It looks like a random crash under load and gets blamed on almost everything else first.
A supply also runs most efficiently at moderate load, and one running near its limit runs hotter, louder and shorter.
As a working rule: total the parts, then choose a supply comfortably above it. The card maker's recommended system wattage already accounts for this and is a reasonable starting point.
Connectors matter as much as watts
A supply with enough total power but the wrong connectors is no use.
- Check how many PCIe power connectors the card needs, and that the supply has that many native cables — not one cable with two ends daisy-chained, which some cards specifically warn against.
- Recent high-power cards use a 12V-2x6 connector. Adapters exist and work, but a supply with the native cable is cleaner and avoids a chain of connections under load.
- Seat that connector fully. A partly-seated high-power connector is a known cause of overheating at the plug. It should click.
Quality, briefly
The 80 PLUS badge describes efficiency, not reliability, though better units tend to carry both. A longer manufacturer warranty is a reasonable proxy for how long the maker expects it to last — a supply with a ten-year warranty is a different product from one with two.
Cheap unbranded supplies routinely overstate their rating. That is the specific case where a failure takes the board with it.
Modular or not
Fully modular means every cable detaches — tidier and easier to build with. It makes no difference to performance. It is a convenience, priced accordingly.
Expected result
A supply with comfortable headroom, the native connectors your card wants, and a warranty suggesting the maker expects it to last.
Never open one
There is nothing user-serviceable inside a power supply, and it holds a dangerous charge long after it is unplugged. If it has failed, it is replaced, not repaired.
Related
Compatibility warnings in the builder, which flag insufficient headroom and connector mismatches before you order.
Read this next
- Choose a graphics card by what you actually run — The card you choose is what decides the wattage and the connectors.
- The PC is completely dead: no lights, no fans — A supply that is failing often presents as a machine that will not start.
- Use the PC Builder, and share or save a build — The builder totals the draw for you as you pick parts.
Still stuck?
If anything here does not match what you are seeing, stop rather than force it. Contact us · Book a repair
Last reviewed 2026-08-19.