Samsung 15W Wireless Fast Charger Duo Pad

I got this dual charger to charge two earbud cases at the same time. The phone/earbud side charges, the earbud/watch side does not. I tried charging a Google Pixel Buds A-Series case (with the earbuds in the case) on each side of the dual charger. Only the phone/earbud side of the charger worked (indicated by a red light on the charger and a yellow light on the earbuds case). I tried charging a new set of Galaxy Bud 3s (with the earbuds in their case) on each side of the dual charger. Again, only the phone/earbud side of the charger worked. I tried charging both earbuds at the same time, one on each side of the dual charger. Again, only the phone/earbud side of the charger worked. I swapped earbud locations on the dual charger. Again, only the phone/earbud side of the charger worked. I tried a phone on the phone/earbud side of the charger and an earbud case on the earbud/watch side. Again, only the phone/earbud side of the charger worked. All of this was done with the included wall plug and USB-C-to-USB-C cable, in multiple wall sockets. Of note: Every time I plugged the charger into the wall, both sides of the charger had a momentary light cycle from red, to green, to yellow, then out.