Micro-servo 9g SG90 not rotating
Servo sg90 is small and can be powered from your computer or laptop connected to the Arduino. The problem does not lie there, but maybe about your connection. Make sure about these things:

Brown is connected to GND
Orange is connected to VCC
Yellow is connected to digital PWM pins.

You could use this code that I am hooking up, with several servos and using external supply but if you try doing the same make sure all the motors are properly grounded.
#include&lt;Servo.h&gt;
Servo ServoBase;
Servo ServoLeft;
Servo ServoRight;
void setup(){
  ServoBase.attach(6);
  ServoLeft.attach(5);
  ServoRight.attach(3);
}

void loop(){
  ServoBase.write(140);
  ServoLeft.write(120);
  delay(1500);
  ServoBase.write(40);
  ServoLeft.write(30);
  delay(1500);
}