I've got a sparkfun 345xl accelerometer connected over 3.3v i2c to an arduino yun.
Everything works fine when the yun is powered by my laptop USB port. The accelerometer triggers, the arduino connects to my iPhone hotspot, and sends an SMS using temboo and twillo.
However this won't work when the yun is connected to a wall outlet USB power source. I've tried an iPad charger, and a 5v 1000ma android micro USB charger. The yun comes on, connects to the wifi hotspot, and I can log into the linino console just fine. However the accelerometer is never triggered.
I'm attaching a picture of the circuit. It's quite simple, and not power consuming, so don't understand why it won't work when connected to a wall source.