I've got one of these sitting next to me as well, though I am also lacking the proper power adapter for it...
I notice that the label on the bottom of the unit is a bit different than mine, most notably lacking the Australian telecom approvals, as well as mine being a "D1001A" rather than "D1009A" The 1001 variant being equipped with dual 1.44Mb floppy drives, and the 1009 having one floppy and a 20Mb HDD
According to the "accessories service manual" I found on the HP Computer Museum the AC adapter should be rated as follows:
Input:
120Vac nominal at 60Hz.
220-240Vac nominal at 50Hz.
29W Typical.
Output:
8.02 to 8.18 Vdc (at 0A, no load).
7.66 to 8.18 Vdc (at2.4A).
Ripple: 0.1 V (p-p) maximum (at 0 to 2.4A).
Current Limit: 2.4 to 2.6A (at 4 to 8.18 Vdc).
The connector itself is a typical type found on most laptops, about 1/4" in diameter with a small pin in the center. I believe (just trying to remember from when I had mine running) that it's center positive. The battery itself is a sealed lead-acid type, 3-cell, 6V battery. These things didn't have a great shelf life, with storage times listed at up to a meager 18 months if fully charged and deactivated, in no warmer than 20C...
How many ports are on the back of that machine? There should be a standard d-sub25 printer port and external monitor (CGA,EGA,MDA depending on hardware setting) in the first bay, probably a blank slot in the second where the HDD controller typically is, then either blanks, RJ-11 (I think) plugs for a modem or 25 and 9 pin d-sub serial ports depending on the options that were included with/added to the system...