GUIDE
How to choose a power supply (PSU) for your PC
The power supply feeds every part of your PC. Too small, and the system can shut down under load. Too few of the right cables, and your graphics card will not even connect. Here is the method BuildPC uses, step by step.
1. Find the peak power of your CPU and graphics card
These two parts use most of the power. For AMD Ryzen CPUs, AMD calculates peak socket power (PPT) as the TDP × 1.35, so a 65 W chip can draw up to 88 W and a 120 W chip up to 162 W. For Intel CPUs, use the “Maximum Turbo Power” on Intel’s specification page; for the Core i5-14400F it is 148 W. For the graphics card, use the power figure from the card maker’s own page (for example, Sapphire lists 304 W for its PULSE RX 9070 XT).
2. Add the rest of the system and some headroom
BuildPC adds 80 W for the motherboard, memory, drives and fans, then multiplies by 1.35 for headroom and rounds up to the next 50 W. This is our planning rule, not an official industry standard, but it keeps the supply well away from its limit.
3. Respect the graphics card maker’s recommendation
Card makers publish a recommended PSU size. Use whichever is higher: the calculated figure or the maker’s recommendation.
Worked example
AMD Ryzen 7 9800X3D (162 W peak) + Sapphire PULSE RX 9070 XT (304 W) + 80 W = 546 W. Multiplied by 1.35 that is about 737 W, which rounds up to 750 W. Sapphire also recommends 750 W for this card, so 750 W is the minimum; 850 W gives extra room.
4. Count the power plugs your graphics card needs
Wattage is not enough: the PSU must also have the right connectors. Many cards use 8-pin PCIe plugs (the RX 9070 XT above needs two), while some newer cards use a single 12V-2×6 plug. Check the cable list in the PSU manual. For example, Corsair’s RM650e (2025) includes one 8-pin PCIe cable plus an adapter cable with two 8-pin plugs, so it can feed three; the RM750e and RM850e can feed four.
5. Make sure it fits your case
Most cases take a standard ATX power supply. Small cases often need the smaller SFX or SFX-L size and have a maximum length. For example, the Cooler Master NR200P V2 takes SFX or SFX-L supplies up to 130 mm long, and the Corsair SF750 (2024) is an SFX unit 100 mm deep.
What this method does not tell you
Wattage and connectors are only part of the story. Build quality, efficiency, noise and how a unit handles sudden power spikes are best judged from independent technical reviews. BuildPC does not test power supplies.
Planning a compact build? Read the small PC build guide.
Specifications come from manufacturer pages and were last reviewed in October 2026. Always confirm them on the manufacturer’s site before buying. BuildPC has no affiliate links and does not track live prices.