OK. after posting all this I realized you have a 3650.  I had one and gave it to my daughter when I got a chance to buy a 3955 cheap.  It's been a year (maybe 2 now?) so my memory is fuzzy, but no, I don't think a 3650 charges through the data port...Let me drop her a note and ask.  Anyway, here is what I found about a cradle for mine:

 (original response)

I have a cradle for mine part number 250181-821. It powers the ipaq, BUT it has a separate power supply that plugs into it. It looks like this

EXCEPT it has another cable running to it that plugs in beside the hard wired cable. The wall wart is by Delta electronics with a number ADP-10SB. Another part number on it is 253628-001. It is
5V 2000mA center pin positive.

HEY! Just found one at http://www.wholesalepdas.com/browseproducts/HP-iPaq-A-C-Adapter-P-N...

One is also listed on ebay right now Item number: 6880035750 which seems to include the adapter to charge the ipaq directly without the cradle