Which class of PD has a minimum power of 4.0 W at PSE?

The class of Power over Ethernet (PoE) devices that has a minimum power of 4.0 watts at Power Sourcing Equipment (PSE) is Class 1. This class includes devices that require moderate power levels, specifically designed for applications that don't consume a high amount of energy. The minimum requirement of 4.0 watts aligns with the specifications set for Class 1 devices, enabling them to operate effectively without exceeding the power supply limitations of the PSE.

Classes in PoE have specific power output ranges that delineate their capabilities. While other classes exist with different minimum power thresholds, Class 1 is explicitly defined as having a minimum power requirement that starts from this 4.0-watt level. Hence, this makes Class 1 the correct answer in this context.