The AC side voltage/frequency doesn't matter as long as you have a wall adapter that works for that situation. The device being charged sees a USB power source and doesn't care what's driving that.

(Also note that many, but not all, common wall-plug USB power supplies are natively designed to work under both voltages. It's usually just matter of having the appropriate plug adapter to connect the pins from whatever sockets are used abroad)

So USB has its own voltage and the 120/230 v doesn’t matter so much with USB?

Yes, the USB cable is carrying 5 (or 9/12/15/20) volts direct current. Thr job of the charging brick plugged between the USB cable and the wall is to regulate AC power down to direct current for USB

The first letter, U, in USB stands for universal. As in, it can take power from anywhere.

I've traveled to France, Malaysia, Hong Kong, Japan, etc and all USB plugs are the same and I can draw the exact same amount of power from them. You might want to buy a travel plug adapter, but what comes out the rectangular USB side is the same

Thank you so much!

Thank You! Makes packing a lot easier

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That isn't why it's called universal. Universal serial bus means common. It was developed to do away with all the different interfaces we had before. Serial, parallel, PS2, gameport, etc. You think having usb mini/micro, Thunderbolt, etc is annoying now, it was atrocious 25 years ago.