There is a chance that your bank may charge an additional fee if they decide to treat your transaction as a cash advance. Most of the time, this can occur if you are using a credit card for the purchase, rather than a debit card.
Simplex does not charge any additional fees apart from the processing fee which is already included in the total cryptocurrency amount you will receive.
The cash advance fee, as any other additional fee (international transaction, currency conversion, etc.), is controlled by the card issuer.
In order to receive more information about any additional fees that you might encounter, it would be best to get in touch with your bank directly.