The external power adapter is NOT a charger. It simply converts household power to USB power at whatever maximum amps the adapter supports.
iPhone, iPad and Mac machines all themselves control their own battery charging. The external power adapter merely determines whether they can charge at fast charge or not as the power adapter determines the maximum current (and hence maximum wattage at industry standard USB 5 volt) the power adapter can supply.
So as long as the power adapter supplies industry standard USB 5V and the minimum amperage for the device it really does not matter whatever brick you have plugged into the wall outlet in terms of quality of charge (whatever that even means, if anything).
The only question is if the amperage of the brick can provide sufficient total power for fast charging or not.