Can I power 12v devices from USB-C?
Yes, your RAVPower-Portable charger uses Power Delivery protocol to increase voltage on Type-C connector. Unfortunately, it looks like the 12-V profile is missing from delivery options, and the charger doesn't support any more flexibility.

The breakout dongle for PD will work only if you attach to it a micro-controller with I2C interface, and program it to send proper negotiating inquires. It looks like the owner of this dongle offers some libraries for that. Still it is unlikely that you will get 12 V output.