I bought a 2nd-hand Lenovo USB-C PSU (ADLX65YLC3D) which indicates a range of voltages (20v, 15v, 9v, 5v) on the label. Tried to charge a few different bicycle lights but the charging indicators did not light up on any of them. I almost tossed it because the 2nd-hand market I bought from is definately dodgy. But then I tried to power a Rasberry Pi and it seems to work on that. So wtf? An a/c adapter either works or it doesn’t. What would cause this: works on some devices but not others? The Rasberry Pi needs 5v just as the bicycle lights. That is the default voltage for USB-c.
Most usb- c pd adapters wont put ouz any voltage on their own. the end device must tell the adapter what voltage they want via the cc pins. on the raspberry pi this is done via resistors between cc1 snd cc2 to get 5v. those pins are most likely unpopulated on your bycicle lights, so they get no power.
This is correct. I made my own USB C to 30 pin adaptors for old iPods and this is precisely how I had to build them.