ChargerLab came up with these renders based on information given to them from inside the production line. The renders show the European version of the charger with rounded pins. The new 18W USB-C charger also seems to be smaller in footprint compared to Apple's current USB-C power adapters.
Image source: ChargerLab
Apple is expected to bundle this USB-C charger with an USB-C to Lightning cable for the three new iPhone models. With this setup, the iPhone can charge to 50% in about 30 minutes!