Im a tad bit confused. I thought regardless of what companies advertised the wattage of their chargers *like this car charger for example is 36W* Ive read the iPhone caps the wattage at 12W even if its higher? Or does this only apply to wireless fast charge?
iPhone 8 and iPhone X can charge at around 18 watts using the 9 volt USB PD spec. you need to use the Apple lightning to USB C cable. This Belkin charger, and many other chargers, support the higher profiles of USB PD. it's the same thing that the new MacBooks use to charge.
you are correct however when talking about chargers that don't do the higher voltages from the USB PD spec. a 2 port charger that advertises 24 watts usually means it can do 24 watts combined.
There are so many ways to confuse these specs, there are going to be so many people buying/selling the wrong things.