Amsterdam tram system payment method?

You can just tap your US credit card (Visa or MC).

Do note though that one should have individual physical credit cards or one shared over multiple devices (one physical card and the same number on a device like Apple Pay or Google Pay on your phone). You can still buy paper tickets on the tram and bus or a GVB ticket machines for the metro.

Does that also apply to trains? I'll be taking a train from the airport to central station around 3pm, then back to airport at night.

Yep.. you can tap in and out at the turnstiles or buy a ticket from a vending machine. More information on tap in/out at https://www.ovpay.nl/en/about-ovpay.

At the airport though, you will need to tap in at the readers (yellow poles) close to the stairs going down to the platform. At Amsterdam Centraal you will have turnstiles with readers. Of course, vice versa when going back to the airport; do not forget to check out at Schiphol.

Got it, thanks. Great to know I don't need a paper ticket!

Schiphol reminds me of Copenhagen where there were no turnstiles (I was shocked) but some pillars where some people were tapping. I had a Copenhagen card for 72 hours so didn't need to do anything, I was told.

Most likely you may have already read it, but AmEx is not accepted.

The tap-in/tap-out poles at Schiphol airport are not obvious, and certainly not if you do not know to look for them. If I recall, when you see the several escalators that go down to the platforms from the main hall, they form a big ring around the set of escalators and ticket machines in the area, so if you make it to an escalator, you may have to backtrack to find one.

If you will have data service for your phone, the NS train app is very helpful for finding the best train option.

Thanks again. I always travel with eSim for cell phone data. I will look at the app but will only take train to and back. I’ll be there on a long layover.
Appreciate the advice on what to look for!
And I always travel with my Amex and Visa. And a debit card to take cash. As well as some dollars for emergency exchange (like when Dublin ATM swallowed my card on a Sunday.

where there were no turnstiles (I was shocked)

You're in for lots of shocks then :-) Not having gates or turnstiles at public transit is actually the norm in Europe. The Netherlands is a bit of an exception here.

“ You're in for lots of shocks then :-) Not having gates or turnstiles at public transit is actually the norm in Europe. The Netherlands is a bit of an exception here.”
In the Netherlands there are only turnstiles at subway/metro stations and most train stations. There are no turnstiles at tram or bus stops.