This updated guide explains ATX power supply form factors, physical fit, common connectors, wattage considerations, efficiency ratings (80 Plus), and regional mains differences. It recommends checking case clearance, choosing a unit with enough connectors, and preferring reputable manufacturers and higher efficiency certifications for long-term reliability.
Why the power supply matters
ATX stands for Advanced Technology eXtended. The power supply is the one component that makes everything else run: if it fails, the PC stops. A poor-quality unit can damage other components or cause instability. Modern desktops demand reliable, efficient power, so choose the supply deliberately.Form factor and physical fit
ATX describes a set of mechanical and electrical standards, not a single size. Standard ATX power supplies typically measure about 150 mm wide × 86 mm high; depth varies from ~140 mm to 200+ mm. Small-form-factor systems use SFX or TFX units, which are shorter and require a matching case or an adapter bracket.Before you buy, check your case specifications for PSU clearance. If you're replacing an existing unit, measure the old supply and compare connector placement and depth. A microATX motherboard uses the same ATX connectors as a full-size board, but small cases may need SFX-type PSUs.
Wattage, rails, and peak vs. continuous power
Estimate your system's power draw (CPU, GPU, drives, fans) and leave headroom for upgrades. Look at continuous (not just peak) wattage ratings. Modern PSUs usually provide a single +12V rail with adequate current, but specifications vary - read the label or product sheet.Connectors you'll need
Modern PSUs include:- 24-pin ATX motherboard connector (replaced the old 20-pin)
- 4+4 or 8-pin CPU/EPS connector (sometimes labeled EPS12V)
- PCIe 6+2-pin connectors for graphics cards
- SATA power connectors for SSDs/HDDs and some NVMe drive cages
- Peripheral 4-pin Molex for legacy devices
Efficiency and build quality
Look for 80 Plus efficiency certification (Bronze, Silver, Gold, Platinum, Titanium). Higher tiers mean less wasted heat and slightly lower electricity costs. Other quality indicators: reputable manufacturer, stable voltage regulation, active power factor correction (PFC), and good warranty terms.Mains voltage and safety
Household voltages differ by region: roughly 120 V/60 Hz in the U.S. and 230 V/50 Hz in much of Europe. Most modern PSUs support 100-240 V auto-switching. Still, check the product spec and safety approvals (UL, CE, etc.) before purchase.Practical shopping tips
Compare wattage, available connectors, efficiency rating, and physical depth. Read recent reviews and pick an established manufacturer. Spend a little more on a well-reviewed, efficient PSU - it's the foundation of a reliable system.FAQs about Atx Power Supplies
Will any ATX power supply fit my microATX motherboard?
Most microATX motherboards use the same electrical connectors (24-pin ATX, 4/8-pin CPU) as full-size boards, but the case may require a smaller SFX PSU. Check your case's PSU form-factor support and depth before buying.
How much wattage do I need?
Estimate the combined power draw of your CPU, GPU, drives, and fans, then add headroom for peak load and future upgrades. Use online PSU calculators or vendor charts and prefer a supply that delivers the required continuous wattage.
What does 80 Plus mean and which level should I pick?
80 Plus certifies efficiency at typical loads. Bronze or higher is a good baseline; Gold or Platinum offers better efficiency and typically higher quality components, but at a higher cost.
Are modern PSUs compatible with international voltages?
Most modern PSUs support 100-240 V auto-switching, but verify the spec sheet and required safety approvals (UL, CE) if you'll use the unit in a different region.
Do modular PSUs make a practical difference?
Yes. Modular or semi-modular PSUs let you connect only the cables you need, improving airflow and reducing cable clutter inside the case.