Earlier @laobaiTD posted a photo of the suspected charger dedicated to iPhone 12 on the Internet, which was displayed as 20W. It is faster than the 18W USB-C charger attached to the iPhone 11 Pro.
Today, there is another message from MySmartPrice, which shows on the Norwegian electronic product certification database that on February 28, 2020, a USB-C charger model A2305 was certified. The model is exactly the same as the photos leaked by @laobaiTD earlier, so it is speculated that the charger for iPhone 12 will be increased from 18W to 20W.
At present, the iPhone 11 Pro/11 Pro Max is equipped with an 18W USB-C charger, but the iPhone 11 is still equipped with a 5W slow charger. It is temporarily unknown whether the 20W charger will be used on the entire iPhone 12.