Exercise 5.3: Sizing a Workstation Power Supply

A Scenario-Based Calculation

A scenario-based exercise where you calculate the required PSU wattage and select an appropriate model for a high-end AI workstation build.
Author

Chuck Nelson

Published

October 20, 2025

1 Purpose

This exercise challenges you to move from theory to practice by sizing a Power Supply Unit (PSU) for a realistic, high-performance AI workstation. Instead of testing an existing component, you will analyze a list of parts, research their power needs, and make an informed recommendation for a new PSU, justifying your choice based on wattage, efficiency, and form factor.

2 What You’ll Accomplish

By the end of this exercise, you will be able to:

  • Research the power requirements of individual computer components.
  • Calculate the total estimated power draw for a complete system.
  • Apply a safety headroom and select a PSU with appropriate wattage.
  • Recommend a PSU efficiency rating and modularity type based on the system’s needs.

This exercise maps to the following program and course learning outcomes:

  • Program Learning Outcomes (PLOs):
    • 3. Apply terminology and numeric or system concepts: You will perform power calculations and apply concepts like wattage, efficiency ratings, and form factors.
  • Course Learning Outcomes (CLOs):
    • 4. Configure hardware and basic network components: Selecting the correct PSU is a critical configuration and system design task.

This exercise develops the following skills, which align with the O*NET SOC Code 15-1232.00 for Computer User Support Specialists.

Learning Objective O*NET KSAs Technologies Used
Research component power needs. Knowledge: Computers & Electronics
Skills: Reading Comprehension, Research		 Web Search
Calculate system power requirements. Knowledge: Computers & Electronics
Skills: Critical Thinking
Abilities: Mathematical Reasoning		 PSU Calculators

3 Scenario

You are a system builder at a custom PC company. A client has approved the following list of components for a powerful AI and machine learning workstation. The final piece of the puzzle is the Power Supply Unit. Your task is to analyze the build, calculate the power requirements, and recommend the ideal PSU.

Here are the selected components:

Component Model
Case Fractal Design Meshify 2
CPU AMD Ryzen 9 7950X
Graphics Card AMD Radeon Pro W7900
Motherboard ASUS ProArt X670E-Creator WiFi
CPU Cooler Arctic Liquid Freezer II 360 AIO
RAM G.Skill Trident Z5 Neo 64GB (2x32GB) DDR5
Storage 2 x Samsung 990 Pro 2TB NVMe SSD

4 Your Task

Complete the following steps and record your answers and justifications in your Microsoft Teams Student Notebook.

  1. Research Power Draw: Use the internet to find the power consumption for the two most power-hungry components: the CPU (TDP) and the Graphics Card (TBP/TGP).

  2. Estimate Total System Draw: Create a simple power budget. Add the CPU and GPU power draw together. Then, add a reasonable estimate for the other components (Motherboard, RAM, SSDs, AIO cooler, and case fans). A good estimate for these other parts combined is between 100W and 150W.

  3. Calculate Required Wattage: Add a 25% safety headroom to your total estimated system draw. This ensures the PSU is not running at its absolute maximum, which improves efficiency and lifespan. Round your final number up to the nearest common PSU wattage (e.g., 850W, 1000W, 1200W).

  4. Make Your Recommendation: Based on your calculations and the build, recommend a PSU by specifying the following four characteristics. You must justify each choice.

    • Wattage: (Your calculated value from Step 3).
    • Efficiency Rating: (e.g., 80 Plus Bronze, Gold, Platinum). What is the best balance of price and performance for a high-end workstation?
    • Form Factor: (e.g., ATX, SFX). What does the chosen case require?
    • Modularity: (Non-Modular, Semi-Modular, or Fully-Modular). What is best for cable management in a high-end build?

Recommended PSU Specification

Here is a breakdown of a recommended solution. Your answer may vary slightly, but your justification is the most important part.

1. Power Draw Research: - AMD Ryzen 9 7950X CPU: Has a default TDP of 170W. - AMD Radeon Pro W7900 GPU: Has a Total Board Power (TBP) of 295W.

2. Estimated Total System Draw: - CPU: 170W - GPU: 295W - Motherboard, RAM, SSDs, Cooler, Fans: ~125W (estimate) - Total: 170 + 295 + 125 = 590W

3. Required Wattage Calculation: - 590W * 1.25 (for 25% headroom) = 737.5W - Rounding up to the nearest common PSU size gives us 850W.

4. Final Recommendation:

  • Wattage: 850W. An 850W PSU provides more than enough power for the calculated 737.5W peak load, ensuring the PSU operates efficiently and quietly without being stressed.

  • Efficiency: 80 Plus Gold. For a high-end workstation that will run for long hours, a Gold-rated PSU is an excellent choice. It ensures high power efficiency (90% at 50% load), which reduces electricity waste and produces less heat, leading to a more stable and longer-lasting system. A Platinum rating would be even better but often comes at a significant price premium.

  • Form Factor: ATX. The Fractal Design Meshify 2 is a standard ATX case and requires a standard ATX power supply.

  • Modularity: Fully-Modular. In a high-end build focused on performance and aesthetics, a fully-modular PSU is essential. It allows the builder to use only the necessary cables, dramatically improving cable management, increasing airflow through the case, and resulting in a much cleaner final build.

Example Recommended PSU: A Corsair RM850e (850W, 80+ Gold, Fully-Modular, ATX) or a SeaSonic FOCUS Plus Gold 850W would be an excellent choice for this build.

5 Reflect and Review

ImportantReflection: 3-2-1

Now that you have completed this exercise, reflect on your experience in your Microsoft Teams Student Notebook:

  • 3 factors you must consider when selecting a PSU for a new build.
  • 2 reasons why adding a wattage “headroom” is a best practice.
  • 1 question you still have about PSU specifications or features.
TipCheck on Learning

Answer these questions in your notebook to solidify your understanding:

  1. Besides the CPU and GPU, what are two other components that draw power from the PSU?
  2. Why is it critical to check the case specifications before choosing a PSU form factor?
  3. What is the primary benefit of a higher 80 Plus efficiency rating (e.g., Gold vs. Bronze) in a workstation that runs 24/7?
  4. For a first-time builder who is concerned about easy installation and clean aesthetics, what type of PSU modularity would you recommend and why?
Back to top