What determines the fee?
The main variable is the Energy required by the token contract. Recipient state matters: sending to an address that already holds USDT usually requires less Energy than sending to an address with no USDT balance.
Network parameters and smart-contract behavior can change, so treat fixed figures as an estimate and confirm the order price before payment.
How delegated Energy lowers the cost
Instead of burning TRX at the protocol rate, you rent the required Energy from a provider. The provider delegates the resource to your sending wallet, and the subsequent USDT transfer consumes that resource.
Your saving is the difference between the cost of the Energy order and the TRX the network would otherwise burn. Coinfira savings can be up to 65%, depending on the transaction.
A practical checklist
Confirm that the wallet is a self-custody TRON address and is active. Check whether the recipient holds USDT. Buy the appropriate Energy amount for the sending address. Then send USDT from that same address within the resource window.
Do not buy Energy for a centralized exchange deposit account expecting the exchange to use it. Exchanges send withdrawals from their own hot wallets and set their own withdrawal fees.