The A5+s USB port can provide around 500mA, which is standard for high powered USB 2.0 devices; however, both the iPad and the iPhone require around 1000mA to charge with the screen on (the iPad's included USB charger actually provides around 2100mA to speed up charging with the screen on).  If your iDevice is at a higher battery level it should work fine to plug it in to the A5+ to maintain the battery while listening to music (with the screen on it will always show "not charging").  If the battery is low though, we'd recommend plugging it into the charger that came with it.