It will never fast charge on a OP5T but it should slow charge just fine. Only later OP phones (8 onwards) will medium fast charge on standard USB-PD (15 or 18W

It will never fast charge on a OP5T but it should slow charge just fine. Only later OP phones (8 onwards) will medium fast charge on standard USB-PD (15 or 18W not the full 35 or 65W). Eg a laptop charger or Qualcomm QC 3.0 or higher. But slow charging should work on pretty much anything. Having said that, USB-C has a protocol for active devices connected to each other that agrees which device will deliver power to which. Previous USB standards didn't need that as the cable has different ends and this would determine this based on the port type. USB OTG however started to break this assumption based on plug type but needed a wiring change. So they made it fully dynamic in USB-C but only if active devices are on both ends. Then they'll negotiate. If an active device just sees 5V from a dumb power supply without any kind of signalling it should always slow charge only. It will assume a dumb USB1 power supply meaning 5V at 500mA so 2.5W charging. Perhaps this needs some configuration in your case though I've seen every computer charging my oneplus just fine. Try to select USB charging only mode in your oneplus. A USB condom should also work, it's a cable that only permits the 5V through and nothing else. It's used to avoid public chargers from trying to access your files in secret. As for technical write-ups hackaday has done some in the past but they're a news site so it's not too easy to find back.