Ok this passive ethernet splitter was making me question if I really understood how things work, but apparently you can only use one of the devices at the same time. So ok, not sure why the hell you would buy such a thing https://www.amazon.com/NOBVEQ-Ethernet-Splitter-Connector-Adapter-Black/dp/B0C16CCN7Y/
I'd love to have a tiny ethernet switch in my apartment's telecom box—currently ethernet out from my cable modem is patched over to give me a wired connection in one other room. But there's no power to plug anything in, even if it did fit
Amazon.com