The USB Type-C spec defines a much simpler mechanism than Power Delivery for ports to advertise their current capability. Type-C Current works by just putting a different pull-up resistor on the CC line of the Type-C connector to indicate different source currents. Combined with the pull-down in the sink, this creates a voltage that indicates how much current the sink can draw from the source. Table 4-27 from the USB Type-C spec shows these voltages.

I just pushed a commit adding support for Type-C Current as a fallback when Power Delivery communications fail. This means the PD Buddy Sink is now capable of getting up to 3 A at 5 V for your project even from non-PD power supplies.