I have two 7's. Tested side by side one with iPhone and other iPad charger the iPad charger charges way faster.Well there's no 70% increase in speed, sorry. I have tried with both iphone 7 and previous models. It charges at pretty much the exact speed as with a regular charger.
Up-to 70% increase in charge & speed is only till the point where it starts trickle charging. At that point it doesn't matter which charger you use.
Likewise it's been tested quite thoroughly that the iPhone 7 can take 1.76A from fast chargers including those intended for Android.
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I do not know why your device is not charging quicker, but the general consensus of everyone else and the myriad of tests readily available all have a consensus that says otherwise.
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