The on screen volume display is NOT part of the OS. When you installed it sounds like you used an Ultimate Disk rather than Dell's installation so you do not have any of Dell's "extras". Those extras would include the program to display volume on screen.
You can probably
download the original program from Dell or you can try a substitute like
3RVX which is what I use and love. What I love about 3RVX is that it is customizable so I can make my own volume bars.
If I had to guess I would bet it is this client/management instrumentation program: