I recently bought a HDMI switch so I can share one monitor between my mac mini and PS4. Although the switch comes with a power plug, I was told that it is unnecessary unless I'm laying really long cables, something over 20m. And just as the sales guy said, it runs off my PS4 fine without power. With the PS4 running, I can also switch to the mac mini channel and it'll display fine. However, once I switch off the PS4, the screen just cuts out. It seems like the mac mini either isn't powering the switch, or is not sending enough power to the switch. I could just plug it in, but I'd like to know if there's another solution.