USB port in Ireland/UK with American devices

Almost certainly. I have numerous times.
https://www.ricksteves.com/travel-tips/phones-tech/electric-adapters-converters

Plug away. The only problem you might face is slow charging.

A USB port is the exact same world round.

I have used available USBs but prefer to use the appropriate adapter and my Samsung fast charger for my cell phone when possible.

Note that some larger devices (particularly late-model Ipads) can't really charge up at the "standardized" USB rate. They may just function, without gaining any charge, unless they are very low to begin with. Big Apple chargers technically violate the international standard for maximum current from a USB port.

Note that some larger devices (particularly late-model Ipads) can't really charge up at the "standardized" USB rate.

There is no standard USB rate. That said, the current can vary on different USB ports. Some are 1A ports while others are 2 or 3 A ports.

Plugging a 2A device (such as a tablet) into a 1A port means it will charge slowly (if at all). But you can plug a 1A device (such as a phone) into a 2A or higher device. It will self regulate.

There are also fast charge ports, but those are rarely provided in public spaces.

So your phone will charge on these public ports but your tablet may not.

The big problem is ports and chargers that are cheaply made and don’t actually do the job. They are the ones the blow the electronics. So don’t get your charger at some kiosk in the middle of the mall.

Cindy, your statement is not correct. There are multiple industry-maintained USB Standards, which can be found, along with their current ratings in Amperes, here:

https://en.m.wikipedia.org/wiki/USB

The first paragraph is enough to support my point. But page down for the current limits. Looking at a USB port in a seat-back is not enough to know WHICH level stardard it is, alas.

The fact that they are not ANSI or CE Standards does not mean that they do not exist.