How to choose power supply
The SG90 is an RC servo, and can easily be controlled by an Arduino using the servo library.

The SG90 is intended (like most servos) to be operated from battery voltage around 5V.  They usually work just fine on anything from 4.5V to 6V.  

I doubt that an SG90 will really draw 1A.  I am currently running a couple of much heavier servos (30kg as opposed to the 1.5kg of the SG90) on a single 5V supply rated for 2A.  I am operating the servos at the upper limit of their load rating, and the 2A power supply is good enough.

A 5V powersupply rated for 2A would be more than enough to handle your little SG90s.

A single 5V , 1A supply would probably handle all four of them  at the same time just as well. 

I in fact ran a couple of 10 kg sevos from a 5V, 1A supply for a while.  That did tend to over heat and shut down, though.



I see in a comment that you connected it to a battery and it didn't run.

That is correct.  A servo will not run when only connected to power.  It MUST have a valid control signal as well.  You can generate that control signal with your Arduino.  Refer to the Arduino reference page I linked above.  It includes some tips on connecting your servos to an Arduino, as well as a couple of examples. (The examples include code, a schematic diagram, and a wiring duagram.)

These servos will not rotate like a regular motor.  They are intended to position the shaft in response to the control signal.  They rotate only 180 degrees, and with the correct signal you can set the shaft to any position in that range.



Servo ratings are weird.  In the datasheets they are rated in newton centimeters of torque, sometimes in inch pounds.  Then they advertise them in kilograms.  A 1.8 newton centimeter servo is advertised as a 1.5kg servo.   The conversion from newtons to kilograms is OK, but the centimeter is ignored - even though that is the thing that makes the difference between a force and a torque.