Dan's seeing the issue I saw reported in many reviews. Essentially the phone's power draw is higher then what the chargers can provide, due to the LTE, CDMA/GSM and GPS chips all being active.

Generation one chips for new cellular data standards are typically very power hungry. In the past, this was hidden because they went into dedicated data only devices like the USB adaptors for laptops. Now they are being crammed into smartphones, before a second or third generation can come along with power optimizations.