Retrieve Windows WiFi passwords

Windows remembers every Wi-Fi password you've ever used. The following is how it reconnects to those networks.

To display all your saved Wi-Fi networks, in PowerShell run:

netsh wlan show profiles 

Then run 

netsh wlan show profile name="PROFILE" key=clear" 

Naturally, replace PROFILE with the profile from the first command's output.
Look at KeyContent for the network's password.