My HTC draws whatever current it needs from my new car adaptor, up to what I assume to be a maximum of 1 Amp, which is the output limit of that adaptor. My previous adaptor had an output limit of only 0.5 Amp (500mA), so did actually fail to charge if the phone was also in use and drawing a high load.
The charger can be a limiting factor, but I haven't seen a 500mA charger for sale in quite a while now, so all posts I've made assume a charger of 1A or more.
If you tied the data pins on such a charger, the phone is likely to pull MORE than the 500mA the charger is rated for, and likely cause failure in the charger due to heat.
The charger itself is RATED for a certain current, it is the phone or tablet that actually decides what charging rate to use. This is usually 500mA in USB mode, and 1A for a phone in AC mode, or 2A for a tablet in AC mode.
I've not had to short any USB pins together to make it function properly like this, so maybe these pins are already shorted on the adaptor because the manufacturer knows that they needed to be... wouldn't all car USB adaptors be supplied like this as standard?
Then the charger will have the pins connected. Try a multimeter.
Why not supplied as standard? Ask a manufacturer.
I think you'll find most, if not all, genuine phone-specific chargers do indeed have the data pins tied, just like in your wall charger. It is the generic car adapters that do not always have this done.
What does AC stand for, if not Alternating Current?
AC alone does stand for that, but in the context of every post I am using it to define the mode in which the phone charges, as displayed in the charging menu of an Android phone, and as most people refer to it.
Edit: Just a bit of further information.
Although the phone decides the charge rate, depending on the quality of the charger, it will have it's own built in maximum controlled by an IC, and so only provides say 700mA, despite the phone "asking" for 1000mA.
There is a simple test you can do as you have an Android phone, connect your Sony Xperia T up to the charger, and check the battery settings on the phone, if it says "AC Power", or similar, then the pins are tied already. This means your issue is the charger itself not being able to supply a high enough current. If your settings screen says "USB Mode" or similar, then an adapter/connecting the data pins should solve your issue providing the charger you purchased is rated for 1A or more.
For reference, two of the cheaper chargers I purchased off eBay already had the pins tied, the more expensive charger with better quality and efficient circuitry did not have the pins tied.