I understand Samsung wanting people to reuse their old chargers, but why even include a charging cable with the phone that can't be plugged into a charging block? My cable is the C charging plug on both sides. The dumbest **bleep** I've seen in a long time! I am highly disappointed and upset. This is just another way for them to get more money from people by making them purchase a charger.
my cord into the adapter and then adapter into a brick with a regular USB port.
The S21 requires PD 3.0 for super fast charging. PD, Power Delivery, is a USB-C spec, not USB-A. USB-C allows for the higher voltage and current needed for the fast charging.
So if you want to use a PD 3.0 compatible charger it's going to be USB-C. Whether the cable is included for that reason or for transferring data I don't know but I do know that I use the cable both on my charger and for the initial SmartSwitch data transfer from my Moto to Samsung.
Galaxy S21 Ultra 512g(VZW), Galaxy Book (original, VZW), Tab S4, Galaxy Watch3 (VZW)