I absorb the pain so you don’t have to. If you have a fairly new Dell computer from the Dell Business line of offerings (as opposed to the Home machines), and run into a blocking bug that prevents you from updating from Windows 10 version 1809 to Windows 10 version 1903, here’s a possible solution.
If the update fails immediately with an error that preinstall.cmd scripts could not run, it is likely that the Dell Data Security software is blocking the update. But…you will likely not be able to uninstall all of that software. Some of the elements have very deep hooks into the system, and using the uninstall programs settings page will not work. In addition, there are installed components that do not register as standalone programs, so you can’t remove them with a simple uninstall option.
The solution is that Dell makes a tool to remove all of these components, but you have to call Dell and get to the team that handles the Data Security software. They will make sure that you are not using the encryption and data security tools (NOTE: if you remove the Dell Data Security and Encryption software, you can’t access encrypted data, but unless you are in an enterprise that is managing a lot of Dell machines, odds are that you are NOT using any of those tools — this issue appears to happen only if you have ordered a Dell machine from the Business line, where data security is a selling point, rather than the Home line). The tool Dell provides quickly removes the offending data security tools, and the Windows update seems to work without a hitch thereafter.
If this has been driving you nuts, I hope it helps. I separately note that there are a lot of blocking issues that could stymie a Feature Update, like driver compatibility, etc. This is only for update failures that never start because the preinstall.cmd scripts cannot run.