Choosing a power supply

1. Step 1 of 2

   How many watts

   Add the CPU and graphics card power figures together, then add roughly 150 W for everything else. Add a further 30 per cent of headroom on top of that total.

   The headroom is not there to supply power — it is there for efficiency and transient spikes. A PSU is most efficient at around half its rated load, and modern graphics cards produce brief spikes well above their nominal figure.

   In practice: a build with a mid-range card wants 650 to 750 W, and one with a high-end card wants 850 to 1000 W.

2. Step 2 of 2

   What else to look at

   Use the warranty period as a guide. Manufacturers offer ten-year warranties only on designs they trust — a more reliable signal than the efficiency badge alone.

   Modular cables are convenient but do not affect power quality. They are an assembly convenience, worth paying for mainly in a cramped case.

   If your card uses a 12V-2x6 connector, choose a supply that meets ATX 3.1. That standard accounts for the transient spikes modern cards produce, so the protection circuits do not shut the machine down without cause.

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