The standard size for most mid-tower and full-tower cases.
Before clicking "buy" on your power supply, run through this mental checklist: pc power supply compatibility
If you are building a high-end gaming rig with the latest generation of graphics cards, an ATX 3.0 PSU offers better compatibility and longevity than a legacy unit. The standard size for most mid-tower and full-tower cases
The first hurdle is physical size. Most modern cases are designed to house the standard power supply. However, if you are building in a smaller chassis—like a Mini-ITX case or a low-profile home theater PC (HTPC)—you need to check the specific form factor supported. pc power supply compatibility
: Aim for a PSU that provides at least 20-30% more wattage than your calculated total to handle power spikes and allow for future upgrades.