Well, usually if a credit card is charged in home currency, the payment receiver's payment provider calculates the exchange rate (usually with a rate beneficial for them) and then charges your CC issuer in the currency that your CC is billed in (while you still have to pay your CC issuer's foreign currency fee). This process is usually referred to as "Dynamic Currency Conversion" or DCC.

If you have your CC charged in foreign currency, your CC issuer will do the conversion, at the standard rates which are usually much more beneficial for you.

Most foreign CC providers will give you the option of paying in your home currency or the local currency (and you should always select the local currency), however, the SBB machines don't seem to provide that option.

You can easily tell whether a transaction "fell victim" to DCC - first of all, the CC pin pad will display the amount in your home currency, and then your CC statement will not include the exchange rate (because your CC issuer doesn't know it, they have been charged, for example, in EUR for a euro-zone CC instead of CHF).