The two fast charging schemes are different, so you can only continue down, that is, 20W fast charging, if this is not supported, then continue to be compatible, such as 18W, or even 10W.
Considering that the two fast charges have a certain intersection point, so as long as they are in the same program, the charging will have no impact. It has no effect on mobile phones.
But this is only in theory, how Huawei's charging protection depends on their own control, just like Apple's mobile phone, the third-party charger did not go to the certification of the direct hint of unsafe accessories. At present, Huawei can not do so strict, under the same charging interface, the same can be rushed into, even higher than the compatible charging power of several. Simply put, with OPPO's 65W fast charge to Huawei's 40W fast charge mobile phone, the actual charging power may be about 30W, that is, it cannot reach Huawei's maximum value, and it is impossible to safely follow the charging agreement.
Oppo's fast charge and Huawei's fast charge their protocols are different, and they cannot be interoperable, and the charging power cannot reach the effect of fast charge after interoperable.