Stupid question :

- Have had a look if there's no background process stuck at 100% CPU usage that sucks the energy away ?
(Either install a command-line tool like htop or a native GUI app like Crest)

For example : a synchronisation that take a long time when you power-up your phone.

Or : some android process eating CPU like it's candy.

That might be a reason why at the first attempt (while the process is still running) it's only charging 8% per hour (most of the energy goes into the CPU, with only a little bit left over to charge the battery), and only charges normally much later on further attempts (once the process has finished clogging the CPU).



Also :
- Modern phones like the Xperia throttle their charging speed based on the voltage they detect on the USB port. If the voltage drops too much maybe the phone is pulling too much out of the charger and thus the phone slows down the charging speed.
So a charger advertises 1.5A charging current max, but when plugged in the phone, only 4.8v are seen on the microUSB cable, so the phone will throttle down, e.g.: eventually settling for only 800mA charging current-

Bad quality cable can mess with this detection : older phone will still charge, but due to poor conductors (thin wires for 5V and GND inside the cable), there's resistance and the voltage drops causing your Xperia to slow its charging speed.

If you don't have access to the original cable (or if it is worn down due to use) it might be good to buy a new one, a 'thick' cable with thicker conductor on the 5V and GND.

Also, some charger (usually advertising "smart IC" and stuff like that) can attempt to boost a bit the voltage on their side (emitting 5.2V instead of 5V) to counter-act resistance in the cable (it helps a bit).

Also, before "USB Power Delivery standard", there wasn't really an official way to advertise max current for a charger (except de facto fumbling with resistors across the D+ and D- data lines).
So it might be that the other phone you tested correctly sunderstand the maximum output of the charger, but the Xperia happens not to speak the exact same signaling dialect and falls back to the safer 500mA