as "Spitzwei" already said, the plug on the device side has a "somewhat small and filigree" size... But it does correspond to the size of a small plug, as can be found in many universal power supplies with interchangeable adapters...
And now for the nitty-gritty: universal power supplies rarely deliver 19 volts... But notebook power supplies (most of them, anyway) do... If such a power supply is available (worn out or not...), then take it (with 19 volt output voltage), mount the cable with the AC adapters POLRICHTIG (!!!!) to it, and you can use it with the RAVPower.
Have fun and success!
As far as I know, the power supply unit is not offered separately. Also stupid is the chosen plug (on the device side), an absolutely impossible size or an extremely filigree mini part. None of my three! universal power supply units have a corresponding adapter.