There are many meters that measure actual power flowing through a USB-C port. This is one example, but you can search for “USB-C power meter” at your retailer of choice to see the multitude of options.
Do check the 240W power adapter thread for caveats as right now it seems there’s some issue with how laptop’s embedded controller manages the power consumption for different part of the system that leads to system bouncing very annoyingly between high performance and half-performance modes as the battery charge state oscillates around 90% charge state making the 180W charger a much better choice still.