Just in case you are missing the Apple 87W USB-C Power Adapter that originally came with the Apple 15" MacBook Pro (2018), you can still charge the Mac quickly using other chargers such as the Apple 61W USB-C Power Adapter that shipped with the 13" MacBook Pro (2017) through USB Power Delivery 2.0 technology.
We first attached the 61W USB-C Power Adapter to a Thunderbolt 3 based USB-C connector on the Apple 15" MacBook Pro (2018) using the Mac's own supplied Apple USB-C Charge Cable (2m) accessory. While the starting voltage quickly stepped up from 5 volts to reach around a 20 volts rail, the Mac took a while to only begin pulling current up to 3.1 amps although just briefly to initially charge at 62.9 watts (20.3 volts @ 3.1 amps). The current then rapidly dropped down to near .5 amps but immediately picked up to increase gradually despite bouncing up and down the entire time. Over the quick changing current, the Mac could be seen to frequently pull around 3 amps to max out charging at about 61 watts (20.3 volts @ 3 amps) with the 61W charger. Click here to download the trace captured by the GRL-A1 power analyzer to see more details.
The Mac uses aggressive power management schemes such that even while the charger was connected to the Mac, the current repeatedly went up close to 3-3.1 amps at repeated intervals, which is also similar to that seen with its own 87W charger.