It's get password by system api without root, may works on Samsung devices.
NOTE: It's used to show the password saved/joined on your phone.
After install, goto WiFi settings, click the SSID to open info dialog.
You can also long click the password to copy it.
If it's not works for you, send me the Xposed Log with Settings.apk/dex will be helpful.
WiFi Passowrd, Xposed for all devices (see above for details)
Xposed Package Name: com.czbix.xposed.wifipassword
Current Stable Version: 1.15
Last Updated 2018-01-16