3.6 Given a scenario, install the appropriate power supply.
📘CompTIA A+ Core 1 (220-1201)
A power supply unit (PSU) provides electrical power to all components in a computer. The wattage rating tells you how much power the PSU can deliver. Think of it as the “maximum energy capacity” of the power supply. It is measured in watts (W).
1. Why Wattage Rating is Important
Every computer component needs power:
- CPU – The processor consumes a lot of power, especially high-end models.
- GPU (Video Card) – High-performance graphics cards require significant power.
- Motherboard and RAM – These need less power but still contribute to total consumption.
- Storage drives (HDDs, SSDs) – Each drive adds to the total power requirement.
- Peripheral devices – USB devices and expansion cards also draw power.
If the PSU does not provide enough wattage:
- The system may fail to boot.
- Components can become unstable or crash.
- The PSU can overheat and fail.
If the PSU has too much wattage, it’s generally safe, but it can be more expensive and less energy-efficient.
2. Calculating Wattage Needs
To pick the right PSU, you need to calculate the total power requirement of your system. Here’s the step-by-step approach:
- List all components in the system (CPU, GPU, drives, fans, peripherals).
- Check their typical power consumption (usually listed in watts).
- Add a safety margin (usually 20–30%) to account for future upgrades or peak usage.
Example (exam-style):
- CPU: 65 W
- GPU: 150 W
- Motherboard + RAM: 50 W
- Storage drives: 30 W
- Fans + peripherals: 20 W
Total = 65 + 150 + 50 + 30 + 20 = 315 W
Add 30% safety margin: 315 × 1.3 ≈ 410 W → Choose a 450 W PSU.
3. Common Wattage Ratings for PSUs
Power supplies come in standard wattages:
- 300–400 W → Small or office computers (basic tasks).
- 450–600 W → Mid-range computers with one GPU and a few drives.
- 650–850 W → High-performance gaming PCs or workstations.
- 1000 W+ → Servers, multiple GPUs, or extreme gaming rigs.
Exam tip: Know that higher-wattage PSUs are needed for systems with power-hungry CPUs and GPUs.
4. PSU Efficiency and Wattage
Modern PSUs have efficiency ratings (80 Plus Bronze, Silver, Gold, Platinum, Titanium). A more efficient PSU:
- Uses less electricity to deliver the same wattage.
- Produces less heat, helping cooling.
- Is more reliable under load.
Even if a PSU is rated 500 W, an 80% efficient PSU delivers only 400 W effectively, so efficiency is important when calculating wattage.
5. Exam-Focused Key Points
- Wattage rating is the maximum power the PSU can supply to the computer.
- Always calculate total system power needs before choosing a PSU.
- Add 20–30% extra wattage for safety and future upgrades.
- Higher wattage is not dangerous, but low wattage can cause instability.
- Efficiency ratings affect how much power the PSU can deliver effectively.
✅ Quick Memory Tip for the Exam
Think: “Enough wattage keeps my PC stable; extra wattage keeps it safe and ready for upgrades.”
