Which of the following is the MOST likely to cause a server power supply fan to fail but allows the power supply to still be functional?

Dust buildup inside a power supply fan can obstruct the fan blades, clog bearings, or increase friction, leading to fan failure (e.g., stopping or reduced speed) while the electronic components of the power supply itself may continue to function initially. This scenario allows the power supply to remain functional for a period, though overheating risk increases.

A power surge is more likely to cause catastrophic failure of the entire power supply unit, including its electronic components, rather than just the fan while the rest remains functional.

Excessive humidity can lead to corrosion or short circuits within the power supply, which would likely affect the entire unit's functionality, not just isolate the fan failure.

While high temperatures can stress a fan and contribute to its failure over time, they are more of a symptom of a failing fan or inadequate cooling rather than the direct cause of the fan's mechanical failure itself, which is often precipitated by dust.