I recently purchased an iPhone X, and along with it I also purchased a 29W USB-C Power Adapter and a USB-C—Lightning cable. This setup is supposed to enable Fast Charging of the iPhone X.
However, always when plugging in the iPhone X to this setup, the phone gives a way the "charging" sound notification twice. Is this normal behaviour?
I don't get the double sound notification when plugging in via normal Lightning-to-USB-A to another 12W adapter, nor when connecting the phone with a Mac.
I'm thinking the second sound notification may have something to do with switching over to Fast Charge, but I haven't been able to find a definite answer. Or perhaps some component is faulty?
This thread (external link) has people asking the same thing:
https://forums.imore.com/iphone-x/396144-fast-charge-apple-ac-adapter-cable-double-sound.html
Best Answer
The double chime is definitely a bug rather than a feature. it's caused by the switch from regular charging speed to the fast charging speed. when the power adapter takes too long to make the switch (I guess we're talking about 10s or 100s of milliseconds), the iphone thinks it got disconnected and reconnected again.
That explains why some chargers cause iphones to make a double chime and some don't. Mine is a 3rd party charger and I've never had a double chime on my iphone 11, even though I'm 100% sure it's double charging (I connected it through a wattage meter and I can clearly see that the switch from 5W to 18W happens)
edit: you can refer to this video (not mine, but underlines what I just wrote)