Which of the following conditions may indicate an issue with a transformer?

A decreased voltage output from a transformer is indeed a strong indicator of an issue. Transformers are designed to either step up or step down voltage while maintaining a relatively consistent current based on the power equation (Power = Voltage x Current). If the voltage output is lower than expected, it suggests that the transformer may be underperforming, which could be due to several factors such as core saturation, winding issues, insulation breakdown, or increased impedance due to overheating.

In a properly functioning transformer, you would expect to see the voltage output consistent with the transformation ratio. Deviations can lead to inadequate power supply for connected loads, potentially causing further complications in an electrical system. Correct voltage output is crucial for maintaining the efficiency and safety of the overall system, making this a key sign of transformer health and functionality.