In my quest to make the PD Buddy Sink the best possible device for getting power from USB PD chargers, the next step is to add support for more types of PDO. I still don't know any chargers that advertise variable or battery PDOs, but I just found evidence of one that supports the very exciting Programmable Power Supply PDO from USB PD 3.0: https://www.diodes.com/assets/Evaluation-Boards/QC4-27W-Class-A-Reference-Design-User-Guide-Release-1.0.pdf
Now the question is, "how the heck do I get one?" I haven't found any evidence that these exist beyond the linked PDF and some Chinese articles that don't seem helpful. If anyone out there can tell me how I could get my hands on one of these evaluation boards, I'd really appreciate it!