220-1201 Hardware Practice Question
A user reports that a desktop PC randomly shuts down during intensive tasks such as gaming or video rendering. The technician notices the power supply is rated at 500W and the system includes a high-end GPU with a TDP of 250W and a CPU with a TDP of 125W. The PSU has a single 12V rail rated at 30A. Which of the following is the MOST likely cause of the shutdowns?
⚠ Common exam trap
The trap here is focusing solely on the PSU's total wattage while ignoring the 12V rail's amperage limit, which is the actual bottleneck.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The PSU's 12V rail is insufficient to meet the combined power demand under load.
The 12V rail provides power to the CPU and GPU. With a 30A rating, it can supply 360W, but the combined TDP of the CPU and GPU is 375W, exceeding that capacity. Under intensive tasks, the PSU's overcurrent protection may trigger, causing shutdowns. The total wattage is less relevant than the 12V rail's amperage. Upgrading to a PSU with a higher 12V amperage would resolve the issue.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The PSU's 12V rail is insufficient to meet the combined power demand under load.
Why this is correct
The 12V rail supplies power to the CPU and GPU, which are the primary consumers. A 30A rating on the 12V rail provides 360W (12V × 30A). The combined TDP of the GPU and CPU alone is 375W, exceeding the rail's capacity before accounting for other components. This causes voltage drops or overcurrent protection shutdowns during heavy loads. Thus, the 12V rail is insufficient, making this the most likely cause.
- ✗
The PSU's total wattage of 500W is too low for the system's components.
Why it's wrong here
While 500W total may seem low, the critical factor is the 12V rail's amperage. The total wattage includes 3.3V and 5V rails, which are less relevant for high-power components. A 500W PSU could theoretically handle the load if the 12V rail had sufficient amperage. However, with only 30A on 12V, the rail is the bottleneck. Therefore, total wattage alone is not the primary issue; the rail distribution is.
- ✗
The GPU requires a dedicated 12V rail that is not available on this PSU.
Why it's wrong here
Modern PSUs often use a single 12V rail, which simplifies power distribution. A dedicated rail is not a requirement; a single rail with sufficient amperage can power multiple components. The problem here is the amperage capacity, not the lack of a dedicated rail. Claiming a dedicated rail is needed is a misconception. Thus, this is not the most likely cause.
- ✗
The CPU and GPU are drawing power from the 5V rail instead of the 12V rail.
Why it's wrong here
CPUs and GPUs primarily draw power from the 12V rail, not the 5V rail. The 5V rail typically powers drives, USB, and some motherboard components. If they were drawing from 5V, the system would likely not function at all due to insufficient power. This option is technically incorrect. Therefore, it cannot explain the shutdowns under load.
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Power Supply Units and Connectors
Key term
CAN
A CAN (Controller Area Network) is a robust vehicle bus standard designed to allow microcontrollers and devices to communicate with each other without a host computer.
Key term
GPU
A GPU (Graphics Processing Unit) is a specialized processor that handles the rendering of images, video, and animations for display output and can also be used for general-purpose parallel computing tasks.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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