I am using a Lenovo Desktop PC & have 3 Monitors setup.
The Desktop machine has x2 Displayport Ports which allows me to use 2 of my 3 monitors.
I bought a UGA-2KHDMI adaptor to allow my 3rd screen to work.
Once I plug my adaptor in, my 3rd screen works and my existing 2 screens do not work.
Once i unplug my adaptor, screen 1 and 2 turn back on.
I have tried the following:
Different USB port
Different Pluggable Adataptor
Pluggable 1st then 2 Displayport adaptors.
The only way I have got all 3 to work is by using 3 Pluggable adapators.