I have a 3 port USB-C charger from Aukey that for the past weeks worked well with my Nexus 5X when used with an old ATX power supply as power source.
I found critical reviews on Amazon (link to US website, but same type of issues on DE and IT as well) where the product stops working or even fries the phones after some time.
I am using exclusively the USB-C port, the other ones cannot charge the Nexux 5X as fast. I am using the original Nexus 5X USB-C cable, not the one provided by AUKEY (it is said to be low quality).
I decided to take it apart and I measured the voltage on the power pins of USB-C while charging and while the charger is powered by 12.2 V from a DC-DC power supply. The source is therefore cleaner than a car electric circuit would be.
I measured with this conditions on the output port 5.10-5.38 V. The tester gives me 5.01 on a LM7805 used as calibration.
Nexus 5X is not Quick charge 3 compatible, therefore it does not negotiate voltages continuously variable above 5 V, in theory it should only jump to 9 V but I haven't seen it, even if the charger could provide it.
Will the 5.4 V damage my Nexus 5X, as it happened to (other) smartphones from the reviews? After all, USB tolerates up to 5.25 V only.