The US-8 can be powered by 802.3af/at, 48V passive PoE, or the included power adapter. When the US-8 is powered by 802.3at PoE or the included power supply, port 8 supports 48V (2-pair) PoE passthrough to deliver up to 12W of power.
PoE passthrough options for the UniFi Switch 8 Ports
Power Input 802.3af In -> PoE Passthrough No PoE Out
Power Input 802.3at In -> PoE Passthrough 802.3af Out
Power Input Power Supply (Included) -> PoE Passthrough 48V Passive Out