Problems with powering pixhawk cube

Hello everyone,

i use a pixhawk cube to control an application which uses two servos. For power supply i have a usb connection and an external power adapter delivering 5V/ 2 Amps to supply the servorail and pixhawks power-port. I dont have something like a power module for voltage or current sensing, i just feed it directly into the power-port. As long as i run the pixhawk and its programme (i use simulink px4 toolbox) with both connected it works as it should work. But when i try to run it only with the external power supply it soon will exit and shuts down with a blinking yellow/orange led. Does anyone know what might be the reason ?
What does an orange blinking or solid led mean?

Thank you for any advices