Well....I picked one of these up recently, actually I've been doing some digging on these quite a bit and have a LOT of information to share (picture below).
The FMA3500 case style started being used on the 386DX based FMA3300. I don't know much about this one.
The FMA3500 came in 3 submodels:
FMA3500 - This was the standard model, had a Casio MD800TT50-C1 9.4" 640x480 grayscale STN LCD. No Trackball, has a 4-pin power plug. Shipped with 4MB or 8MB of RAM on 30 pin SIPS (4x sockets) with a 486DX-33 CPU. Has Cirrus Logic SVGA Graphics. Looks like tthis shipped in both white and gray cases.
FMA3500SX - This was a 486SX version of the same machine, 25MHz I believe instead of 33MHz. Same features and seems to be extremely uncommon compared to the FMA3500 or even the FMA3500C.
FMA3500C - This came in 2 versions, a Passive Matrix version with a Sanyo LCM-553022NTK 10-ish inch 640x480 FSTN LCD which is suprisingly nice (mine has this panel), and the other a 9.4" Active Matrix Panel that's offset in the screen enclosure. Same specs as the regular 3500 otherwise. Has a Varta battery fro CMOS (I need to replace/fix mine). I recall seeing one or two on e-bay with the 4-pin power adapter, but mine and the majority I've seen use a regular barrel power jack at 19vdc (though I've run mine as low as 12vdc and all the way up to 24vdc).
All three used the same 12v NiCAD Screw-On Battery pack. There's also a trap-door on the back for an expansion module/Docking Station that goes on in place of the battery and offers 2 ISA Slots (in lieu of the lack of PCMCIA slots on this macine).
It seems the 3500 and 3500C were available with and without a tiny 2-button trackball located above the power slider. Mine has this, and it's decent, but nothing to write home about. Well made though, the rollers are metal. But that trackball itself is just slightly smaller than a pea.
I use the cheap multi-voltage generic "Laptop" power supply from E-bay that I paid $15 for a few months ago with mine. It works great. Even charged the original NiCad and I got about 30 minutes out of it before it developed some kind of a short and stopped working. What's also cool is re-celling the power packs is pretty easy as the battery pack is modular and has a molex plug on the end. Probably could throw NiMH on there if you wanted.
I also put the driver-pack for this up on my website as I saved the drivers I found on the hard drive and zipped them up.
Here's a picture of it loading Windows 3.1. Turns out some kind of travelling engineer from China used this thing. Mine was sold as a BSi model.