I haven't really messed with the DIMMs yet (well as a starter, this laptop isn't exactly the easiest to work on, but I've seen way, way, way worse thankfully), they're still the original ones that came with the machine, although I swapped them (DIMM 1 in slot 2 and DIMM 2 in slot 1),when I got the laptop (as only 128mb was being recognized), I'll try cleaning the contacts with Isopropyl Alcohol and see how this goes.
If that don't work, I might just swap them for 2x256mB DIMMs and call it a day.
By the way, I found something pretty neat:
https://www.hp.com/ecomcat/hpcatalog/specs/F2337WT.htm I wonder how HP didn't remove that page (as it's often the norm these days, they purged anything legacy, and others will follow suit, such as Intel

good thing that the Web Archive wayback machine is a thing).
I've also seen that there was other models of Omnibook XE3s, of which I can't find anything about them, I'll list them here:
- Omnibook Xe3 "GC" (the one I have, seems to be the most common version, Intel Pentium 3/Celeron, S3 SavageIX/MV)
- Omnibook Xe3 "GD" (AMD Duron/Athlon? Frequency unknown, Trident CBXP Graphics w/ 8mb VRAM)*
- Omnibook Xe3 "GE" (AMD K7 Duron or Athlon)*
- Omnibook Xe3 "GF" (Intel Pentium 3/Celeron, Intel 830MG graphics (??)
About the GD and the GE, I could not find anything on them, the only reference I could find is in some kind of manual:
https://www.manualslib.com/manual/71748 ... ml?page=18But I also found this chart (from some HP documentation) showing the different Omnibook Xe3s variations, it's sure handy given that the XE3 is a obscure system!
Proud owner of a Shuttle HOT-555A 430VX motherboard and two wonderful retro laptops, namely a Compaq Armada 1700 [nonfunctional] and a HP Omnibook XE3-GC [fully working :p]