T-Power Ac Adapter for Royal SSC-240013US 440004454 440004454 7-25V DC AC Adapter Class 2 Charger Power Supply

I bought this charger to replace an adapter that I apparently threw away. My handvac is an older model, but I hated to throw it away and buy a new one. I took a chance and purchased this charger, which said it was compatible with the Dirt Devil model #440004454 hand vac. So far it's performed perfectly!

Am I missing something here? I ordered this as a direct replacement for a Royal SSC-240013US charger for a Dirt Devil 15.6 volt hand vac. The charger that I received states that it has an 8-10 vdc output as opposed to the 7-25 vdc in the item description. There has been a lot of back and forth with the supplier and it appears that they don't offer a 7-25 vdc charger but I am failing to understand how this one can properly charge my hand vac.Two things. The vendor is taking it back for a full refund and in looking into this deeper I found that a 1.2v nicd battery requires a charging rate of 1.5v to charge properly. Using that information, and since the Dirt Devil has 13 cells, this puts the required charging rate at around 20 vdc.