I think it would be beneficial to add what is VOOC to the main thread.
The VOOC (Voltage Open Loop Multi-step Constant-Current Charging) Flash Charging system is a rapid-charge technology created by OPPO Electronics, which, at present, is able to charge certain OPPO devices from 0 to 75% in just 30 minutes (Wikipedia)
Is this specific for Oppo devices or does it have any benefit for Apple devices (or any other) ?
I think VOOC is technically superior to Power Delivery as it moves the DC-DC conversion from the phone to the charger so the phone is cooler.
Cells naturally during recharge raise their voltage needs and lower their current needs, so the perfect charger does exactly that.
Most phones tell the charger to take a fixed voltage and slowly lower their current, they then must do the DC-DC conversion in the phone, that means the power inefficiency heat by-product is within the phone, but with VOOC it is outside the phone.
The difference is the thermal throttling of use of a phone competes less with charging, so the average performance can be higher while charging.
It also means you can push more Watts, recharge faster, as you have less heat from the cells to compete with the heat from voltage conversion.