The most likely cause is that the power supply units are failing due to moisture-related internal corrosion. When humidity is high, condensation can form inside the PSU, leading to capacitor leakage or small internal shorts that prevent the PC from powering on. This is a classic symptom of a degrading power supply, not a grounding issue, since you’ve already verified the outlets are properly grounded. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your ability to distinguish between environmental factors and electrical faults—a common trap is to blame the wall circuit or inrush current, but the humidity correlation points directly to PSU degradation from moisture. Remember the memory tip: “Damp PSU, no boot for you”—if the problem worsens on humid mornings, suspect internal corrosion in the power supply before chasing ghosts in the wiring.
220-1101 Power Supply Practice Question
This 220-1201 practice question tests your understanding of power supply. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A small office has several desktop PCs that intermittently fail to power on in the morning. The issue is more common on humid days. After checking the wall outlets, you find they are properly grounded. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The power supply units are failing due to moisture-related internal corrosion
A failing power supply can be sensitive to humidity, causing internal shorts or capacitor leakage. Inrush current from multiple PCs on the same circuit could also be a factor, but the humidity correlation points to PSU degradation. Proper grounding eliminates outlet issues.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 power supply units are failing due to moisture-related internal corrosion
Why this is correct
Humidity can accelerate corrosion on PSU components, leading to intermittent startup failures, especially after the system has been off.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The building's circuit breaker is tripping due to overload
Why it's wrong here
If the breaker tripped, PCs would not power on at all until reset, and the problem would not be intermittent or humidity-dependent.
✗
The CMOS battery is dead on each PC
Why it's wrong here
A dead CMOS battery causes time/date resets but does not prevent the PC from powering on.
✗
The power button is stuck on each case
Why it's wrong here
A stuck power button would cause continuous power-on attempts, not intermittent failures, and is unlikely to affect multiple PCs.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 220-1201 NAT questions on configuration and troubleshooting.
Power Supply — This question tests Power Supply — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The power supply units are failing due to moisture-related internal corrosion — A failing power supply can be sensitive to humidity, causing internal shorts or capacitor leakage. Inrush current from multiple PCs on the same circuit could also be a factor, but the humidity correlation points to PSU degradation. Proper grounding eliminates outlet issues.
What should I do if I get this 220-1201 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 220-1201 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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