Bandwidth from servers belonging to the same account is “pooled.”
If you have 1 VPS with a 4000GB quota, for example, and 1 ARP Thunder™ server with a 2000GB quota, you get 6000GB in total to use in whatever distribution you like.
One VPS can use all 6000GB and the other server can use 0GB, or vice versa, or any combination in between; as long as the total transfer does not exceed 6000GB, you’ll be under your bandwidth quota.