A helper script for access to App.config by PowerShell

Config.ps1

<##
 # Config.ps1
 #
 # (c) 2017 koohq. Licensed under CC0.
 # https://creativecommons.org/publicdomain/zero/1.0/legalcode
 #>

function Initialize-AppConfigFile
{
    [CmdletBinding()]
    [OutputType()]
    param(
        [Parameter(mandatory)]
        [string]$Path
    )

    Add-Type -AssemblyName System.Configuration
    [AppDomain]::CurrentDomain.SetData("APP_CONFIG_FILE", $Path)
    [Configuration.ConfigurationManager].GetField("s_initState", "NonPublic, Static").SetValue($null, 0)
    [Configuration.ConfigurationManager].GetField("s_configSystem", "NonPublic, Static").SetValue($null, $null)
    ([Configuration.ConfigurationManager].Assembly.GetTypes() | where FullName -EQ "System.Configuration.ClientConfigPaths")[0].GetField("s_current", "NonPublic, Static").SetValue($null, $null)
}

function Import-AppConfigFile
{
    [CmdletBinding()]
    [OutputType([PSCustomObject])]
    param(
        [Parameter(mandatory)]
        [string]$Path
    )

    [xml]$config = Get-Content -Path $Path -Raw

    $appSettings = New-Object System.Collections.Specialized.NameValueCollection
    $config.SelectNodes("//appSettings/add") | foreach { $appSettings[$_.key] = $_.value }

    $connectionStrings = New-Object System.Configuration.ConnectionStringSettingsCollection
    $config.SelectNodes("//connectionStrings/add") | foreach {
        $connectionStrings.Add((New-Object System.Configuration.ConnectionStringSettings @($_.name, $_.connectionString, $_.providerName)))
    }

    [PSCustomObject]@{
        AppSettings = $appSettings
        ConnectionStrings = $connectionStrings
    }
}