My xiaomi portable fast charger clearly charges my girlfriend’s iPhone faster than my high end android device. Doesn’t matter which port, which cable or which android phone. It starts by charging fast but as soon as I plug her phone the fast charging speeds go straight to hers and mine just chargers very very slowly.
I’ve got the impression that this may be on purpose or at least has some clear explanation.
Any thoughts?
Based on your description, it just might. See what happens when you plug in your phone second, maybe it just prioritises whatever device as plugged in last.
It’s possible that the iPhone requests a high charging voltage that your phone doesn’t support (iPhones do 9V@2.2A or 5V@whatever they can get). If your phone is charging at 15V@2A for fast charging and an iPhone plugs in, there’s a chance it needs to step down the max voltage to 9V, which in turn your phone may not support, stepping down your phone to 5V.
It could also just be shitty charging software only capable of negotiating with one USB port at a time.
I don’t see what Xiaomi has to gain by selling chargers that don’t charge their own phones faster than iPhones. I doubt it’s intentional.