Yes, the system will charge by USB 3.2, but a 30W adapter is going to be very slow at charging -- and won't run the system at full power.  The  default adapter is 65W -- you need a 65W adapter to charge the system in normal time, and run the system at full power.  
Hello. I am new to a Latitude 3420 and wanted to know if it is possible to charge it through its USB-C port using a portable charger (car or cell phone). The USB-C port on the laptop only has a Data symbol, it does not show the Thunderbolt icon. I have 30W chargers for car (Anker) and cell phone (Moto), I don't know if they will be enough or which one would be correct. I don't know if I could damage the laptop by trying these chargers.   Thank you very much
Latitude 3420 USB-C charging