Are you using a 100W rated USB-C cable? The one that DJI supplies with the 'fly more combo' kit isn't rated for 100W - you'll never get 100W in with that cable. The other issue could still be the powerbank . Not all powerbanks can...
The 3S charging cradle determines the input charging wattage - not the output of the charging brick. So, a 1000W brick would still only supply 100W. There is a handshake going on between the brick and the charging cradle (assuming the brick was...
DJI also makes a 100W charging brick - compatible with the 3S. This is common knowledge. You can view it here;
Buy DJI 100W USB-C Power Adapter - DJI Store
This time, actually LOOK at the links I've provided.
So let me make this as clear as...