How to choose proper power supply for 8 servos on Adafruit shield with Arduino Uno controller
The vendor pages that you link to do not provide any indication as to what the  running current is for the servos. The manufacturer web page is no better. There is probably a good reason that they do not provide this information considering the the current draw of a servo is so variable depending upon applied voltage and the mechanical load linked to the spindle of the servo. 

The manufacturers also make consideration of the typical audience that uses these type products. If they specified a current requirement it may be used as a hard fast number by some users and the then turn into a customer support nightmare when users blame them for the numbers being either way too high or way too low.

Without actual current draw information it will be difficult for you to calculate the size of power supply that you will actually need. So you have two basic options to use.


You can use a brute force technique to provide a power supply that can deliver way more current than you would ever need and wire it up with hefty sized wires to prevent voltage drops.
You can characterize the current draw for your servo in your application by making measurements. Set your voltage and then operate the servo in a manner that mimics its actual usage. In some cases you may be able to make these measurements using a digital multimeter in current measuring mode which will work for steady state conditions. To get a grip on the surge current requirements you typically place a small valued resistor in series with the GND line of the servo (0.1 ohms for example) and then use an oscilloscope to monitor the voltage drop across this resistor in dynamic conditions. Once you know the voltage drop you divide that by the resistor value to determine current flow.


Lastly you will need to look at the operation scenario of your whole setup with all the servos. Not all servos are likely to be drawing worst case current at the same time. Some are likely to be idle drawing nominal current while others are levering against some load and drawing more current. There may also be some that have reached a mechanical limit and stalled drawing maximal current.