What's the right adaptor for iPhone 12 Pro charger?

Specification us same as any USB-C spec. 5 watts or greater.

This 20W is recommended (If British shown, may need to change country)

https://www.apple.com/uk/shop/product/MHJF3B/A/20w-usb-c-power-adapter

You have two choices:

• Go to apple.com then go to iphones, go to accessories and look for the iphone 20 Watt charger brick. If there is one in your currency you will see the price and shipping.
• Buy any good quality 20 Watt charger with USB-C socket that fits the cable that came with your phone.

That is 20watts or more