Hi;
I think I understood you in your first post. What you wrote now makes me believe I understood you alright. Maybe I was the one who did not write well... ;-)
I use the Brazilian AC adapter that used to come with the HP3x series sold here (HP31, 32, 33, 34, 38). They all share the same AC adapter model. Mine has ID # 82119B and has a 115 - 230 Vac input select switch and delivers 9.1 Vac (I measured it right now) with a maximum of .9 Watts output power (written on it). I've been using this AC adapter in my HP25 for more than 9 years and the calculator works fine. The HP25 originally uses the same AC adapter that comes with the HP21, so I concluded the HP3x series' AC adapter would work with the HP21 as well.
About the connector: my suggestion was just to keep the original cord for future restoring.
I remember I measured the output voltage from an original HP2x AC adapter and it looked fine for me using the HP3x series adapter. Maybe I thought, at that time, that the 1 Vac diference from both adapters would not be representative for the internal HP2x (woodstock) charger circuitry.
Is it O.K. for you? My HP25 still charges the batteries (they get a bit warm when charging) and works till they are exhausted. Also, the AC adapter itself works smoothly, gets a little bit warm.
Hope it helps. Anyway, if you still feel you should have more answers (and the best policy is waiting for other posts), wait a little more or post again. I'd do that; this little babe demands caution, it's a rare, reliable and well-featured tool.
Best regards and success.