I have an itinerary AMS-FRA-EWR-FLL, it requires an overnight layover at FRA. I notice the tax jumps from a same day MXP-FRA-EWR-FLL by more than 65% (went from $84 to $139). Another MXP-FRA-EWR-FLL itinerary that has an overnight layover at FRA the tax jumps to $99, an increase of $15 from the same day connection itinerary. Though it is much less than the $39 Passenger Service Charge on the same FRA overnight itinerary that departs from AMS.

I am not sure you could see detail taxes / fees breakdown at booking other than the total amount. Next time I would try to find if there is a breakdown before purchasing the ticket.

But on the eTicket and Receipt, the tax break down shows the following:

September 11th Security Fee: 5.60 USD
U.S. APHIS User Fee: 3.83 USD
Germany Passenger Service Charge: 39.90 USD
U.S. Customs User Fee: 6.52 USD
Germany Airport Security Charge: 10.60 USD
U.S. Immigration User Fee: 7.00 USD
Netherlands Passenger Service Charge: 22.10 USD
Netherlands Noise Isolation Charge: 28.10 USD
Netherlands Airport Security Fee: 15.80 USD
Total Per Passenger: 66000 miles + 139.45 USD

I wonder whether a 10 hr overnight layover is still subj to the Germany Passenger Service Charge?