I never use the installer (I just download the zip file), but I tried the installer for the first time tonight because I
can't get the latest version to work and thought maybe that would help (it didn't). Anyway, I got the same issue you did where it got to like 90% and then couldn't download the universal patch (my internet connection is also fine). So the installer must not be connecting properly or the patch isn't where it's supposed to be downloaded from or something (I have no idea, just guessing).
However, you can just apply the patch manually, you don't need the installer to do it. You can
download the patch here and just cut and paste the files into your UFO folder to overwrite the appropriate files. Make sure you have a backup of the original game files first though just in case something goes wrong when applying the patch.