For your Apple iPhone and Apple Watch, consider using Apple's own USB-C MagSafe chargers (which you may already have) with any suitable USB-C Power Adapter or PowerBank. Ideally, the USB-C power source will be rated at 25W or greater.
MagSafe Charger (1m) - Apple
Apple Watch Magnetic Fast Charger to USB-C Cable (1 m) - Apple
All Apple iPad USB power adapters are designed for use internationally with power sources rated to provide 100V AC to 240V AC at 50Hz to 60Hz. Apple iPad USB power adapters also comply with the IEC/UL 60950-1 and IEC/UL 62368-1 standards for use with power sources rated to provide 115V AC at 400Hz (typically found onboard commercial airlines).
While your Apple Power Adapter will be fully usable when travelling internationally, automatically accommodating any differences in AC supply voltage, you may require a simple pin-adapter to allow the Power Adapter to be used with AC power outlets in different countries. For example, a US flat 2-pin connector or Australian 2/3 pin connector will require an adapter for the standard UK 3-pin square socket or European 2-pin socket.
Travel adapters are readily available from AirPorts - and online retailers such as Amazon. By example, from Amazon:
https://www.amazon.co.uk/Australian-Plug-Sockets/s?k=Australian+Plug+Sockets
Using a simple travel adapter with your existing Apple charging accessories (or third party alternatives if they support multiple supply voltages) is likely to be significant more cost effective and flexible than purchasing country-specific Power Adapters within the countries that you may visit. Many good quality travel adapters are designed to be usable in many different countries.
