About USB-C to barrel plug connectors: I think people generally use a "PD decoy" board with that setup, which does Power Delivery negotiation (usually based on the cheap IP2721 chip but you can get a fancier one from ST) with a PD-capable power brick. This way you can easily get 5/9/12/15/20V out of a single decent quality GaN charger.
Now obviously you want to be careful with where you plug it in but it's still quite convenient.
A more advanced way to do this is use an arduino board that can negotiate arbitrary voltage in 20mV steps with a PPS-compliant charger, effectively giving you a tiny lab power supply (although you can't get under 3.3V and the chargers are still a bit pricy).
I am disappointed that the Anker 715 (Nano II 65W) cannot do 12V with PD, but for some reason it is not one of the standard PD voltages. I think it is capable of 12V with PPS, but I am not sure if the decoy cables support it. If you specifically need 12V with PD, make sure to check if your charger supports it.
Now obviously you want to be careful with where you plug it in but it's still quite convenient.
A more advanced way to do this is use an arduino board that can negotiate arbitrary voltage in 20mV steps with a PPS-compliant charger, effectively giving you a tiny lab power supply (although you can't get under 3.3V and the chargers are still a bit pricy).