These USB-C PD trigger boards [0] are just great for purposes like this. They are cheap and available with either a preset voltage like the author seems to use,

These USB-C PD trigger boards [0] are just great for purposes like this. They are cheap and available with either a preset voltage like the author seems to use, or semi-fixed voltage selection (by putting solder-bridges on number of open connections/pads) or - very useful for tinkering - with a set of tiny switches that allow to change the voltage in a few seconds. I think they are very recommended to have in your parts drawer if you like playing with electronics. [0] “trigger boards” because they don’t do anything directly with the voltages and power. They only negotiate with the power supply which combination of voltage and maximum current (and therefore power) it should provide.