To check the proxy settings like ProxyOveride or if it is enabled or not:
Get-ItemProperty -Path "Registry::HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings"
To disable proxy from PowerShell:
Set-ItemProperty -Path "Registry::HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings" ProxyEnable -value 0
To enable proxy from PowerShell:
Set-ItemProperty -Path "Registry::HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings" ProxyEnable -value 1