Looking for tiny 2-ports hub which doesn't need power adapter

Hi,

often I come to a place where there is only one RJ45 ethernet socket
available, but I would like to connect to machines to the network.

Is there a small hub/switch (2 ports would be enough) which could be
plugged into the single wall socket and allows me to plug in 2
machines?

And: Are there any devices of that kind which do not need a power
adapter? Maybe it could take its power from a USB port...

Has anyone seen something like that?

Regards,
Dominik