The Power Supply
Week 7 · Module 7: The Power Supply · Download .docx
Objectives
- Calculate required PSU wattage with 25% headroom
- Identify PSU connectors and their target components
- Interpret 80 Plus efficiency tier ratings
- Compare modular, semi-modular, and non-modular PSUs
Key terms
- 80 Plus
- Efficiency certification: baseline 80%, Bronze 82%, Gold 87%, Platinum 90%, Titanium 92%.
- Modular PSU
- All cables detachable — connect only needed cables for clean cable management.
- EPS connector
- 8-pin (4+4) CPU power connector providing +12V to the VRM.
- PCIe power
- 6+2 pin connector delivering up to 150W per connector to a GPU.
- Wattage headroom
- Operating the PSU at ~75% rated capacity — best efficiency and lifespan.
The concept
The PSU converts 120V AC to stable DC: +12V (CPU, GPU, drives), +5V (USB, legacy logic), +3.3V (RAM). The 80 Plus program certifies efficiency at three load points. Higher efficiency = less wasted heat and lower electricity bills. To size: sum all component TDPs, multiply by 1.25 for 25% headroom. Modular PSUs remove unused cables for cleaner builds. Always turn the PSU rear switch off AND unplug before working inside — standby +5VSB is live any time the cord is connected, even when the PC is off.
Worked examples
Common mistakes
- Matching PSU wattage exactly to component TDP — leaves no headroom and stresses the PSU.
- Leaving the rear PSU switch on while working inside — +5VSB standby remains live.
- Using a non-modular PSU in a compact case — excess cables block airflow.
Self-check
Try each one before you look. A miss here costs nothing and tells you exactly what to reread.
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