Whether you travel abroad, in regards to cash withdrawals: the ATM knows the card is from your home country, so it brings up dynamic currency conversion (which is the ATM’s own quoted rate), giving you the option to choose that or continue without it (leaving that up to your home bank instead). For example: you decide to withdraw 300€ from the ATM but the machine’s exchange is 300€ = $410 (which is a rip off).
But, if one continues to not use DCC: the bank does the conversion from their end, in this case it comes out as $358 including a $5 transaction fee (more like $353). The same applies to contactless payments, as at some establishments, the reader will give you a choice between local currency or the one from your home country, do you pick the one that’s already converted or pay in local currency leaving it up to the bank?
Banks will still fleece you on the exchange rate. Ideally you would have a multi currency card so you decide which exchange rate to use and have the cash in the account in the local money.
It’s not hard to find a bank that only charges a 1% fee on the spot exchange rate. You shouldn’t be using a debit card (“cash in the account”) almost anywhere. Credit is so much better.
But the exchange rate is where they fleece you not the card usage fee.
Maybe if you have a bad bank, I’ve checked mine and it’s competitive. April 17 I did a Bandcamp transaction in GBP, charged my Chase card and got <1% difference in USD compared to the mid-market exchange rate on that date. It’s $90.21 on my statement, $89.92 when I calculate it, so +0.3% off the mid-market rate.
If you’re getting anything worse than this, you’ve got a shady bank, and there’s no lack of competition.