Anyone have an lg ultra wide hooked up? 34um95

I have a ps4 hooked up via a hdmi splitter - worked fine with an old hp monitor but noticed today, it only works when the mac is turned on! Even after I unplugged the display port and usb hub, it still went to 'no signal' when the mac sleep - how can it do this when the mac is not connected to the monitor in anyway? Very strange!

Any ideas? Fairly low issue as I rarely use the ps4, especially at my Mac Pros monitor

EDIT - the elgato game capture hd needs usb power so I've now connected...

Anyone have an lg ultra wide hooked up? 34um95