the features tab for power store says the following for shipping:
Real-time shipping rate quotes – shipping providers
-United States Postal Service (USPS)
no where does it mention that you can create other shipping rules.
The available features of PowerStore are on display in the power store demo web site:
the shipping tab of the admin settings page:
displays all of the available shipping options that can be configured.
The power store demo site clearly demonstrates all of the available functionality in PowerStore