Bandwidth from servers belonging to the same account is "pooled."
That is, 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.
1 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.