How many watts your build draws and which power supply you need.
The power supply (PSU) feeds the entire build, and coming up short causes shutdowns under load or hard-to-diagnose instability. We add the maximum draw of your processor and graphics card —the two biggest consumers— plus a base for the motherboard, RAM, drives and cooling, and add headroom for spikes and efficiency. The result is the recommended wattage, rounded to a commercial size.
Headroom is not optional. Modern graphics cards (RTX 30/40/50, RX 6000 and later) produce very brief power spikes that can double their average draw for milliseconds, and a PSU running at its limit protects itself by shutting down. A PSU also performs better and lasts longer working around 50-70% of its capacity, not 95%. That is why we recommend with margin, not the bare minimum.
The 80 PLUS certification (Bronze, Gold, Platinum) indicates efficiency, not quality: a Gold wastes less energy as heat. But the most important thing is to buy a unit from a reputable manufacturer; cheap watts from unknown brands don't deliver what they promise and put the rest of your components at risk.
The calculation adds up the typical load power of each component and then adds headroom. The graphics card and the processor account for most of it; everything else — motherboard, memory, drives, fans, lighting — rarely goes beyond 60-80 W combined. We add a cushion on top because a power supply permanently running at its limit neither performs well nor lasts.
That headroom is not superstition. Modern graphics cards produce very brief power spikes, lasting milliseconds, that can double their rated draw. A PSU with no margin reads that spike as a short circuit and trips its protection: the machine shuts off mid-game, with no blue screen and no error to explain anything. It is one of the hardest faults to diagnose and it is avoided with headroom and a decent unit.
Efficiency is the next factor. 80 Plus ratings tell you what share of the incoming power reaches your components, and almost every unit peaks around 50% of its capacity. Sizing so your everyday draw lands near that point means less heat, less fan noise and a slightly smaller electricity bill, plus room for a hungrier graphics card later.
Connectors matter as much as watts. Current high-end cards use the 12-pin connector (12VHPWR / 12V-2x6), and adapting from several PCIe cables is a common source of trouble when the wiring is not up to the job. If your card uses it, look for a supply with that connector natively, built to the ATX 3.0 standard or newer.
Finally, quality is not measured in watts. A cheap 850 W unit can be a worse purchase than a high-end 650 W one: what protects your machine is the quality of the internal components, voltage stability and protections, not the big number on the box.
Just below usually works, but with no margin for spikes or the future. We recommend with headroom for stability and lifespan.
It indicates efficiency (less heat and wasted power), not power. Gold is the usual balance; Platinum, for those who want the best.
That is cabling convenience, not performance. A semi-modular unit makes building and airflow easier, but doesn't change the watts you need.
No. A supply delivers the power the machine asks for, not what is printed on the label. An 850 W unit drawing 400 W costs the same as a 600 W unit at that load, and probably slightly less if it is more efficient.
Not mandatory, but a useful filter. Bronze is the sensible minimum today; Gold is the sweet spot between price and efficiency for most builds.
Mid to high-end units typically serve 7 to 10 years, and the manufacturer's warranty is a good hint: a 10-year warranty signals confidence in the internals.