PSU efficiency ratings explained: Bronze, Gold and wall power
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An efficiency rating tells you how much incoming electrical power becomes useful DC output under defined test conditions. It does not reduce a PSU’s rated capacity, and it is not a complete verdict on noise, protections or build quality.
Separate output watts from wall watts
Suppose a PC needs 300 W of DC output. At90% efficiency, the PSU draws about 333 W from the wall:300 ÷0.90. At85%, it draws about 353 W. The difference is around 20 W while that workload is running. These are worked examples, not measurements of a recommended unit.
A750 W supply rated80 PLUS Gold can still deliver its stated750 W output under its rated conditions. Gold is not a percentage haircut on the label. The conversion loss becomes heat, and the actual efficiency changes with load and input conditions.
AC power supplied at the wall
Some input power is lost as heat
DC power required by the components
Read the right certification table
| Level | 20% load | 50% load | 100% load |
|---|---|---|---|
| Bronze | 85% | 88% | 85% |
| Gold | 90% | 92% | 89% |
| Platinum | 92% | 94% | 90% |
These figures belong to the 230 V EU certification category, useful context for UK mains supplies. The115 V table uses different thresholds. Check the exact unit’s certification report rather than transferring a percentage from a different voltage category.
The mid-load result is one point on the curve. A home server spending most of its time at low power may need more attention to low-load behaviour than a gaming PC running a demanding GPU. Neither machine needs to be deliberately loaded to 50% all day.
Calculate whether an efficiency premium is useful
For a hypothetical20 W difference sustained four hours a day, the annual energy difference is 0.020 kW ×4 ×365 =29.2 kWh. Multiply that by your own electricity unit price to estimate the saving. Use the hours at that load, not the number of hours the PC is merely switched on.
For an always-on NAS, repeat the calculation around the normal idle/light workload. For a gaming machine, include the mix of idle desktop and game time. A large purchase premium can take a long time to recover, so connectors, appropriate capacity and fit still come first. This arithmetic helps assess the premium without inventing a household tariff.
Choose the whole PSU, then the rating
Efficiency certification does not establish fan acoustics, voltage regulation, protection behaviour or long-term reliability. Those need the exact product documentation and appropriate test evidence. ATX revision, cable compatibility and form factor sit alongside efficiency in the selection.
Use the PSU buying guide for the shortlist, the complete load and fit plan for capacity and the cable compatibility guide for replacements. For a server, avoid choosing an oversized supply purely to hit a theoretical mid-load point.
Specifications and setup: CLEAResult 230 V EU thresholds · Certification scope.
