Stepper Motor Control

Hi,

I'm going to control a stepper motor with Raspberry PI.

***Motor 42BYGHW609

Rate Voltage - 3.4 V
Rate Current - 1.7 A
Lead Wire - 4

***Pololu A4988 driver

Minimum operating voltage: 8 V
Maximum operating voltage: 35 V
Continuous current per phase: 1 A
Maximum current per phase: 2 A
Minimum logic voltage: 3 V
Maximum logic voltage: 5.5V
Microstep resolutions: full, 1/2, 1/4, 1/8, and 1/16

The main purpose of this post is that I receive useful tips.

If will supply the driver with a phone charger (see image) 12V - 500mA it's ok? Is nesessary a electrolytic capacitor?
If I increase or decrease voltage/current what will wappen?

The stepper will run. But the powersupply is to small for real work. It will get hot, or the driver will stop working, when the voltage drops to much.
-Olaf