I believe it is 6v, but you are aware that one is included in the box with the scanner?
Think he just got AC and DC adapter mixed up... there is an AC adapter but not DC
The DC adapters from the 396T should work as well... will make it easier to find them on ebay etc rather then looking for 396XT dc adapter
If you mean you have this cord: Uniden Online Store - Accessory Detail
then yes, you can use it with the BCD396XT.
If you have some other cord, I cannot advise.
The manufacturer-approved DC adapter has a label that looks like the below. In addition to being electrically compatible with the charging circuit, it minimizes RF interference from the switching mode regulator used.