I have a Pro Mini 328P 3.3V that has an ADXL 345 and a MicroSD Card Adapter properly hooked to it and programmed using an Arduino UNO. I have checked by only connecting the UNO's 3.3V and GND to the Pro Mini's VCC and GND respectively and the Pro Mini works fine taking readings from the ADXL 345 Accelerometer and saving them to the MicroSD card in a "accel.txt" file. But when I connect the Pro Mini to a MicroUSB power supply (pictured below), it powers up but does not record any values, neither it creates the "accel.txt" file in the MicroSD card attached. I have connected OUT+ to the Pro Mini's VCC and OUT- to the GND.
Where do I start debugging this problem from? What exactly am I doing wrong here?