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First of all, I am aware that there is an almost same question in the room here, but which does not solve my problem.

I got my new Macbook Pro 2018 running Mojave 10.14.5.

I got two external monitors with my 2015 MBP which worked fine. Now, being excited about three possible monitors, I got myself another one of the second external monitor and now have three external monitors. Two of them are SyncMaster B2240, the third one reads "NEC MultiSync EA274WMi". No resolution is higher than 4096-by-2304 stated in the specs:

Simultaneously supports full native resolution on the built-in display at millions of colors and:

Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors.

Up to four displays with 4096-by-2304 resolution at 60Hz at over a billion colors.

Now I bought some cheap adapters (which might be the problem? but I want to be sure first) to connect them:

  • Adapter 1 connects the NEC screen using HDMI and contains an USB hub and an ethernet connector.
  • Adapter 2 connects one SyncMaster using VGA and contains an USB port
  • Adapter 3 connects the other SyncMaster using DVI

Now the actual problem is: No matter the configuration (I always plug all three adapters in a slot on the macbook, no daisy chaining), I always only have two monitors working. Regardless the slot, the first two monitors I plug in will be automatically recognized and work, the third one stays dark and recieves no signal.

I tried replacing the VGA adapter with a second DVI adapter I used for the third one, but still the same result.

When I leave all three monitors plugged in, the macbook won't boot anymore. It will keep getting stuck just at the apple logo without a progress bar. When I plug out the adapters, the boot continues. This also happens rarely when only two or one external monitors is plugged in.

Before I buy apple-certified-only adapters, I want to make sure that this is the actual problem of the case. And why should this be the reason to not have something working according to specs?

I also tried the SMC reset (turn off, press Shift + Control + Option + On-Off for 10 seconds), but this reboot afterwards also kept being stuck.

Really appreciate your inputs!

UPDATE: I checked again and it appears that my MacBook Pro is 13 inch, and therefore only supports two external monitors, while 15 inch supports up to four ...

Found the tech specs here which reads:

Simultaneously supports full native resolution on the built-in display at millions of colors and:

One display with 5120-by-2880 resolution at 60Hz at over a billion colors

Up to two displays with 4096-by-2304 resolution at 60Hz at millions of colors

Up to two displays with 3840-by-2160 resolution at 60Hz at over a billion colors

Is there still a way to get three external monitors to work, somehow? Using an adapter?

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