To set the default startup directory when executing admin power shell, use the following command (currently I have my directory set to c:\dropbox\dev)
*PowerShell -ExecutionPolicy Bypass -NoLogo -NoProfile -NoExit -Command "Invoke-Expression '. ''%ConEmuDir%\..\profile.ps1''' -new_console:d:"c:\dropbox\dev"
Make sure to make the change on the tasks tab:
Then set that task as your startup