I actually had an online chat with Dell about the same thing about a week ago. After some attempts to avoid a direct answer, they said that using a charger with the same size adapter and polarity, and a lower voltage, will not damage the PDA. The only negative result is that your Axim will charge slightly slower when in use.
However much I may love the low prices of Dell PDAs, I refuse to pay their high accessory prices. Thus, you just gotta love it when you see a company go out of its way to try and prevent 3rd party competition by creating an abnormal 5.4V adapter, just to have to admit to its customers that its scheme has a huge flaw...you can still use a lower-voltage adapter and spend $20 less!
Enjoy your free Dell accessory! :approve: