Normal USB can only supply 500mA, so when connecting to PC or Power Supply that has not shorted Data + and - from USB, the 'flash' (for fast charge) will not show.
I modified a 2A Power Supply (5V == 10Watts) with an intermediate adapter to shorten Data+ and Data- and it immediately works and charges fast with (up to) 2A.
+
+
Update: Today I had also the problem that always the 'x' was shown, but it was a software problem, I think the charging is somewhat controlled by software. Now I had to restart the device to get it charging again. First time this happened.
Normal USB can only supply 500mA, so when connecting to PC or Power Supply that has not shorted Data + and - from USB, the 'flash' (for fast charge) will not show.
I modified a 2A Power Supply (5V == 10Watts) with an intermediate adapter to shorten Data+ and Data- and it immediately works and charges fast with (up to) 2A.