This iPad mini 2 (Model A1490) is running iOS 10.3 (14E277), which may not be supported by this version of Xcode.
my xcode version 8.2.1 my Device ios version 10.2
You can avoid both the update to Xcode 8.3 (which works only with macOS Sierra) and the Dropbox download from a random link on GitHub, as suggested in other answers. To work with iOS 10.3 in Xcode 8.2.1, follow these steps:
Exit Xcode 8.2.1
Download Xcode8.3.3.xip
from Apple (https://developer.apple.com/services-account/download?path=/Developer_Tools/Xcode_8.3.3/Xcode8.3.3.xip) (requires sign-in)
Unzip ~/Downloads/Xcode8.3.3.xip
(in Finder, double-click)
Copy folder 10.3.1 (14E8301)
from ~/Downloads/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport
to /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport
(in Finder, right click on Xcode.app
and 'Show Package Contents')
Remove ~/Downloads/Xcode8.3.3.xip
and ~/Downloads/Xcode.app
Start Xcode 8.2.1. Done.