the save file is found here
C:\Users\USERNAMEHERE\AppData\Local\Packages\BethesdaSoftworks.FalloutShelter_3275kfvn8vcwc\SystemAppData\wgs\000900000A5964A4_0000000000000000000000007FACC08D\D300C080FD6644088CDEDA5F33ACDE08
CREDIT: To @MrPrecise for help with location