If you want iPhone 12 fast charging facility, you will have to buy a fast charger adaptor for your device. There are many types of charger adaptors based on their power output capacity. You need to check for the power outage capacity such as 20W, 36 W, etc. Based on this power output, you can select the desired charger. The fast-charging ability lies in the charger adaptor and not the connecting wire. Hence you can continue to use the same charger wire but you will have to buy a new charger adaptor for iPhone 12 fast charging.