I have a nVidia 9600 GT (1xHDMI, 2xDVI, 1xDP) and a StarTech USB2VGAE3 adapter.
I had this setup with 2 monitors connected to the DVI ports on 9600GT and 1 to the StarTech. Worked perfectly. StarTech was for email only (this is a work PC). Ran Windows 7 and then upgraded to Windows 10 still all working fine.
I now have 3 new monitors (Dell P2417H with 1xHDMI, 1xDP, 1xVGA). Using DVI to HDMI cables, I managed to get all three displays working. Then after 5 minutes or so, one of the HDMI monitors turned off.
If I remove the StarTech USB cable, it comes back on, and if I plug it back in, goes off again.
Why does this happen when all three were working before? I even rebuilt PC, but still not working!