It seems as if it is starting off at a low voltage when plugged in and then steadily increases over time. Was 15Vdc when plugged in and is now reading over 100 after typing this.
Maybe you missed a decimal point. It does sound like the poweradapter is bad. Do you have another unit that you could use to check? If so, swap the poweradapter and see what happens. You can contact your local Apollo dealer to order a new one, part number SUB-ROT-WALLTR-P.