I do not believe that your concern should be tied up with the differences between the power supply module you own and it's associated Power Supply Unit (PSU) when it comes to using your existing power supply with UK or USA supplied modules. Electronics work the same way around the world and its physics is not impacted by national borders.
A Module that uses 200ma on a +12VDC rail, 50ma on -12VDC rail and 10ma on a +5VDC rail will do so regardless of where it is used in a rack anyplace in the world. Your concern should be placed in knowing what your Eurorack Power Supply module can safely supply on those rails and whether the modules that you are adding to your system fall within those parameters.
You can use this website to build a model of your Eurorack with the PS and Modules you have and the site will generate the list of all your modules and their individual and combine power requirement in order to stay under what you power supply module can deliver. If you see that your module are taking more than what you are able to power them with, you will then be forced to buy additional power supply modules to allow for expansion.
Don't let the AC voltage and frequency source enter into the equation because all of these modules rely on clean rectified, stepped down DC voltages coming from the Power Supply Module(s).
My 120 VAC 60 Hz source and a 240 VAC 50 Hz source in a different country do not matter because the cards are supplied with +12 VDC, -12 VDC, and +5 VDC only. Your Power Supply Unit (PSU) that you plug into the wall should be the only component different between countries with different AC supplies.
Oh, and do not plead ignorance. The first step in learning is the one you have taken.