First look below your computer to find out the service number. Then, find a Windows machine and install the Dell recovery tool that lets you burn or generate the ISO to reinstall your machine. Once you have the ISO, you can open it with 7Zip.

You can then compare that ISO contents with the ISO of the same Ubuntu version to see all the differences.

There is especially the prepackage.dell file at the root of the modified ISO

Mine contains this :

dell-recovery-1.61-somerville5_fish1.tar.gz
dell-service-meta_3_all.deb
gir1.2-mutter-2_3.28.4-0ubuntu18.04.2_amd64.deb
gnome-settings-daemon-schemas_3.28.1-0ubuntu1.3_all.deb
gnome-settings-daemon_3.28.1-0ubuntu1.3_amd64.deb
gnome-shell-common_3.28.4-0ubuntu18.04.2_all.deb
gnome-shell_3.28.4-0ubuntu18.04.2_amd64.deb
google-chrome-stable-74.0.3729.108-1_fish1.tar.gz
kernel-5.0.0-1031-oem-osp1-bionic_fish1.tar.gz
libinput-bin_1.10.4-1ubuntu0.18.04.1_amd64.deb
libinput10_1.10.4-1ubuntu0.18.04.1_amd64.deb
libmbim-glib4_1.18.0-1~ubuntu18.04.1_amd64.deb
libmbim-proxy_1.18.0-1~ubuntu18.04.1_amd64.deb
libmm-glib0_1.10.0-1~ubuntu18.04.2_amd64.deb
libmutter-2-0_3.28.4-0ubuntu18.04.2_amd64.deb
libplymouth4_0.9.3-1ubuntu7.18.04.2_amd64.deb
libqmi-glib5_1.22.0-1.2~ubuntu18.04.1_amd64.deb
libqmi-proxy_1.22.0-1.2~ubuntu18.04.1_amd64.deb
modemmanager_1.10.0-1~ubuntu18.04.2_amd64.deb
mutter-common_3.28.4-0ubuntu18.04.2_all.deb
mutter_3.28.4-0ubuntu18.04.2_amd64.deb
oem-beaver-osp1-melisa-meta_1_all.deb
oem-fix-eth-realtek-disabletlpr8153_1_all.deb
oem-fix-misc-cnl-oem-image-helper_fish1.tar.gz
oem-option-disable-ext4-lazy-itable-bionic_fish2.tar.gz
oem-release_1_all.deb
oem-seventy-percent-brightness_1.5_all.deb
performance-mode-by-default-bionic_fish5.tar.gz
plymouth-label_0.9.3-1ubuntu7.18.04.2_amd64.deb
plymouth-theme-ubuntu-logo_0.9.3-1ubuntu7.18.04.2_amd64.deb
plymouth-theme-ubuntu-text_0.9.3-1ubuntu7.18.04.2_amd64.deb
plymouth_0.9.3-1ubuntu7.18.04.2_amd64.deb
python-configobj_5.0.6-2_all.deb
python-six_1.11.0-2_all.deb
snap-gnome-stack-beaver-osp1_fish1.tar.gz
sosreport-oem_0.1.5-bionic_fish1.tar.gz
sosreport_3.6-1ubuntu0.18.04.2somerville2_amd64.deb
timbuktu-meta_2.1~18.04timbuktu12_all.deb
tlp-config_4_all.deb
tlp-rdw_1.1-2ubuntu1_all.deb
tlp-sensible_1.4_all.deb
tlp_1.1-2ubuntu1_all.deb
xorg-hwe-18.04-1.20.4-1ubuntu3-beaver-osp1_fish3.tar.gz
xserver-xorg-input-wacom-hwe-18.04_0.38.0~0ubuntu1somervile1-18.04_amd64.deb

Also check the folders "updates". You can also make a dump of a pre-configured installation that can be useful. For example a pre-configured Dell Linux has a few more repositories configured...

In the folder /etc/apt/sources.list.d you will find several files :

• bionic-dell-beaver-osp1-melisa.list
• bionic-dell.list
• bionic-dell-service.list
• bionic-oem.list

Checking the contents of those files form an already installed customized Ubuntu will be useful.

Yeah I also think this XML file is key. Most of these are .deb files found in the recovery .iso, but some are .tar.gz files I can't find anywhere. Any idea what these are?