During the LLDP-MED automatic negotiation process, each PD reserves its power requirements. The last device to power on is not the last to get power. If the power budget is exceeded, then the port priority is taken into consideration to determine which device or port gets the power. For Cradlepoint PSE equipment (such as an E3000, or R1900 for example) you can configure each port with a different priority. Cradlepoint devices use low, high, and critical to differentiate priority. If a power budget is exceeded and two devices with the same priority are powered on, the physical port priority determines which gets power.
See this Cradlepoint article on how to configure port priority.