[NAME] The resolutions supported by the Dell S2721DGF are listed on page 14 of the User's Guide. You did not indicate what model Samsung monitor you have so I am not sure what resolution is its native resolution but for the Dell it is 2560 x 1440, but assuming the Samsung is an older monitor I am pretty sure it is not 2560 x 1440. The message you are getting about changing your input timing is from Windows which indicates that your setting for the Samsung does not match your new Dell monitor. To change the display resolution in Windows, go to All settings / System / Display and select the resolution you want under 'Display resolution'. Given that the XPS 8500 is an older computer I am not sure if the BIOS will support 2560 x 1440 for the BIOS and Dell logo display. Usually, the monitor will adjust itself and display whatever resolution it is given, it just may take some time to adjust to that resolution, and given that the Dell logo only displays a short time it may not have time to adjust. You don't need to Dell screen; in some BIOS you can even disable the splash screen. To enter the BIOS, just keep pressing F2 as soon as you turn on the computer. If you can see the Dell splash screen and the spinning circles it is too late and you need to shut down and try again. You also enter the BIOS from Windows 10, Google search 'how to access bios windows 10 without restarting'.
Hello Community! I have an older DELL XPS 8500.  I am in the process of upgrading and have an 8930 on order.  I just purchased a DELL gaming monitor (S2721DGF).  I am used to seeing the Dell Splash Screen as the computer comes up, but it never appears on this monitor.  Eventually the system comes up with no issues, but I am curious where did the splash screen go?  The new monitor is connected to the old graphics card (Nvidia GTX 660) via HDMI.  I am on Windows 10 pro.  
Dell Splash Screen