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Thanks @SamsungGill - I tried that already and in fact it was working on Win 7 at 1920x1080 resolution. Upgrading to Win 10 seems to be the issue. If I use the HDMI port off the laptop it works fine (but it is not a good set up). There is no HDMI port on the docking station.
Just as an update - I tried a newer Dell E-Port Plus docking station just to eliminate the possibility of bad hardware. Completely different results - worse. It gave me no recognition of either the 2nd screen (Samsung) or a 3rd screen (Dell ST2420L). Switching back to the prior docking station I a least get an image on the 3rd screen, but still black on the 2nd. The Display settings shows all 3 screens and the 2nd screen workspace is active (just completely black). Next thing to try is DisplayPort-to-HDMI cables.
I did - DisplayPort 1.2.
I did find a work-around so it looks like my problem may be fixed. I bought a DisplayPort to HDMI adapter and I am connected now from E-Port port 2->DP-2-HDMI Adapter->HDMI cable->Samsung HDMI 1. Wasn't getting a picture and then found the display adapter needed to be changed to 1920x1080 plus it was defaulting to 29Hz refresh.