The Vostro 3910 onboard HDMI is 1.4 and is only supposed to 1920x1200. So you doing 2048x1152 is already beyond what we support. See page 14 in the online Vostro 3910 Setup and Specifications PDF. These are the supported OEM video cards for the Vostro 3910 =7MKYT Nvidia GeForce GTX 1660 Super 4WY5P Nvidia GeForce GTX 1650 Super6KVHF Nvidia GeForce GT730
I've just installed a new Dell Vostro 3910. It has both a display port and a HDMI. I've got two identical Dell U2515H monitors, one plugged into the Displayport, one into HDMI.  Displayport monitor max resolution is 2560x1440HDMI monitor max resolution is 2048x1152 2560x1440 is the native resolution of both of these monitors. The screen definition/quality is noticeably lower on the HDMI monitor.  So how do I get the 2560x1440 on both monitors? Time for a new graphics card or is there a better solution? Thanks!
Vostro 3910 HDMI lower Resolution than Displayport