Yes, you can use the OnePlus Supervooc 100W charger to charge an Oppo smartphone with 80W charging capacity without damaging the battery.

Here are some important points:
- The charger supports multiple charging protocols, including VOOC, which is used by Oppo.
- The device can adjust the charging power and deliver a maximum of 100W, but it will only provide as much power as the connected device supports. If your Oppo smartphone can only charge 80W, the charger will reduce the charging power accordingly.
- The charger has several protection mechanisms, such as overcurrent, overheating and short-circuit protection, to ensure that the device and battery are protected.

It is therefore safe to charge your Oppo smartphone with this charger.