Convert-SecureStringToString.ps1

function Convert-SecureStringToString {
<#
.SYNOPSIS
    Converts a SecureString value back to a plaintext string
.DESCRIPTION
    Converts a SecureString value back to a plaintext string
.PARAMETER SecureString
    The SecureString that you want to get back to being plaintext
.EXAMPLE
    $SecureString = Read-Host -Prompt 'Enter a string' -AsSecureString
    #Let's say you entered the string 'Password' without quotes

    Convert-SecureStringToString -SecureString $SecureString

    Password
.NOTES
    # inspired by: https://gallery.technet.microsoft.com/Execute-PowerShell-Script-38881dce
#>

    [CmdletBinding(ConfirmImpact='Low')]
    [OutputType('string')]
    Param (
        [Parameter(Mandatory)]
        [securestring] $SecureString
    )

    begin {
        Write-Verbose -Message "Starting [$($MyInvocation.Mycommand)]"
    }

    process {
        $UserName = 'domain\user'
        $Credential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $UserName, $SecureString
        Write-Output -InputObject $Credential.GetNetworkCredential().Password
    }

    end {
        Write-Verbose -Message "Ending [$($MyInvocation.Mycommand)]"
    }
}