Brazil Travel money exchange and dni?

[AdrianB]

the banks that transacted my purchases in Brazil charged a foreign transaction fee(and probably a bad conversion rate), my CC company did not but they do not controll the other banks.

This is not how credit card transactions work. Only way they can charge you more is if the conversion is not done by your bank because you chose so on the POS machine. It's when it asks you if you want to pay in "local" or "domestic" currency or similar. If it asks you this and you chose the wrong option or someone else choses it for you, you can get the worse exchange rate.

Fwiw all of my banks show original currency and conversion rate on their statements.