This seems to work fine for POE and connection speed 10/100 (not 1GB)
if you have a remote are with just one ethernet cable and no power for a switch combining two ethernet connections into one seems too work:
Cable Matters RJ45 Splitter Ethernet Cable Share Kit in White 100 Mbps (Must Be Used in Pairs, One Unit On Each End of an Ethernet Cable Run)
You need to put 2 cables into your switch into the concentrator, then one longer ethernet cable and the reverse to 2 POE devices (eg one RPI and one camera)
as long as they run <= 100 Gbit.
I have a camera and an RPI in the tree in front of my house, and one ethernet cable. This solution seems to work fine. Not standard, but no issues.
It works as 100Mbit Ethernet POE only uses 2 pairs and the cable has 4, it is setup to use pair 1&1 for A and pair 3&4 for B
Cost is $12 + . There are different versions available, with single jack and 2 plugs or the other way around.
You always need a pair of the same kind, They are sold in pairs
Karl