A/B Testing PC Power Supply Calculator FAQ
Answers to common questions about comparing PC build wattage, PSU headroom, power spikes, and estimated PSU capacity.
Use these answers to understand the calculator inputs and results. All wattage figures are estimates, so confirm hardware compatibility and manufacturer documentation before installation.
Using the Calculator
Questions about entering build information and comparing results.
What should I include in other components wattage?
Include estimated power for the motherboard, memory, storage, fans, pumps, USB-powered devices, lighting, and similar accessories.
Can I compare a current PC with a planned upgrade?
Yes. Enter the current configuration as one build and the planned configuration as the other.
What PSU wattage should I enter?
Enter the continuous output wattage stated for the PSU, not a wall-power reading.
Power Inputs and Reserve
Questions about CPU, GPU, and transient estimates.
Should I use CPU base power?
Use an expected high-load package-power estimate where possible, because base power may not reflect demanding operation.
Why add a transient power reserve?
The reserve provides planning headroom for brief changes in demand, especially where component power can vary quickly.
Is a larger reserve always better?
A larger reserve produces a more conservative estimate, but it should still be based on realistic input assumptions.
Understanding Results
Questions about load percentage, spare capacity, and recommendations.
What does lowest spare capacity mean?
It is the smallest difference between the PSU rating and either build's reserved load. A negative number means the reserved estimate is higher than the PSU rating.
Is a load below 100% automatically suitable?
No. It only indicates the result is below the entered wattage rating. Connector availability, PSU condition, quality, and hardware requirements also matter.
Why is the recommended PSU rating rounded up?
Rounding up to 10 W avoids presenting a capacity result below the calculated estimate.
Scope and Accuracy
Questions about what the calculation does and does not cover.
Does the calculator measure real-time power draw?
No. It estimates demand from the wattage values you provide.
Does PSU efficiency change the recommendation?
Efficiency mainly changes AC power drawn from the wall. This calculator compares estimated DC component demand with rated DC output.
Does it check cables and connectors?
No. Check that the PSU has appropriate motherboard, CPU, and GPU connectors before using it with a build.
How does the calculator choose a PSU for two builds?
It calculates a reserved power load and PSU requirement for each build, then uses the higher result.
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