My MKR GSM 1400 works fine when connected to a computer (powered USB) and after opening a serial connection to it. It does not when I plug it into a power supply. My power supply is a 5V 3A with a USB adapter.
void setup() {
// put your setup code here, to run once:
//...
while (!Serial);
//...
}
void loop() {
// put your main code here, to run repeatedly:
//...
}
while (!Serial);
in the sketch?