[WNAP-1110] Can I use 802.3af PSE (Power Sourcing Equipment) to power up the WNAP-1110?

No.
The WNAP-1110 supports only 9VDC power Adapter or Passive POE Injector (RJ45 pin 4, 5: + 9VDC; pin 7, 8: Ground). It can not work with IEEE802.3af PSE for its power source.
At the same time, either 9VDC Adapter from the DC-jack or Passive PoE Injector from the UTP port to the device at one time. Use of two power sources will damage the device permanently.