I have two wall chargers with USB output ports. The 1st one works fine when charging my Sansa Fuze 4G. The player behaves just like when charging the Fuze on my computer USB port. I can play tunes while it’s charging, etc.
The second one will display the lightening bolt for a second or so then the lightening bolt disappears and the battery shows to have full charge. Also, the screen says “writing” for a few seconds, then says “Connected” and I cannot interact with the screen (play tunes, etc). The 2nd wall charger works fine when charging other devices.
Just drug out the voltmeter. Measuring between each of the lines and the shielding I get:
1st wall charger - Red(Vcc) 5.1V, White(D-) 2.04V, Green(D+) 2.04V, Black(Gnd) 0.0V
2nd wall charger - Red 5.2V, White (floating), Green 0.3V, Black 0.0V (white is essentially 0.0)
Computer USB - Red 4.9V, White 0.0V, Green 0.0V, Black 0.0V.
I expected that the black lead and the shielding would be tied together electrically but they were not. The plug metal cases on each end of the cable are only connected to the cable shielding. The red lead and the black lead are the two outer most pins in the plug.