Stork and or anyone else,
I've recently lost a output on my graphics card so I used a different output port to run my two screens. However it continues to "lose" a screen on startups which when I disconnect and reconnect it returns. However, I'm now considering replacing the graphics card.
Have any advice? The machine is a dual boot with Windows 10, I do play "some" games but not many. Currently on Sierra with a very stable build. Am considering moving to High Sierra but in no rush.
I assume you suspect a h/w fault when you say you loose output and looking to replace your gfx card ?
It depends on what you want to do with your system.
For example if you are video editing, then your choice fix card depends on which App you are going to use:
Adobe => Nvidia
FCPX/iMovie => AMD
I had a 650Ti it was fine but as soon I tried to use FCPX, it was a dog - very slow rendering, etc. Unusable.
As a test, I tried it with Adobe Premier and it was fine -- not lighting fast but useable. But I do not use Adobe.
Recently I bought an AMD RX580. With FCPX it's great. Very smooth & fast, very useable.
I am on 10.13.4.