Add-Type wrapper cmdlet. UseTypeAlias=$true to avoid type name conflict.when Add-Type called multiple times. See also https://gist.github.com/altrive/6765957

Add-TypeDefinition.ps1

function Add-TypeDefinition
{
    [CmdletBinding()]
    param (
        [string] $Path,
        [string[]] $ReferencedAssemblies = @("Microsoft.CSharp"),
        [string] $OutputAssembly,
        [switch] $IgnoreWarnings,
        [switch] $UseTypeAlias
    )

    $ErrorActionPreference = "Stop"
    if (!(Test-Path $Path)){
        Write-Error ("Specified path '{0}' is not exists" -f $Path)
    }

    if ($Path.EndsWith(".cs"))
    {
        $files = New-Object IO.FileInfo($Path)
    }
    else
    {
        $files = Get-ChildItem -Path $Path -Filter "*.cs" -Recurse -File
    }

    if (($files -eq $null) -or $files.Count -eq 0){
        return
    }

    #Merge C# code files to import definitions
    $sb = New-Object Text.StringBuilder
    foreach ($file in $files)
    {
        #Write-Verbose ("Add C# type definition from file '{0}'" -f $file.Name)
        $content = Get-Content $file.FullName -Raw
        $sb.AppendLine($content) > $null
    }

    $params = @{
        ReferencedAssemblies = $ReferencedAssemblies
        IgnoreWarnings = $IgnoreWarnings
    }

    if (![String]::IsNullOrEmpty($OutputAssembly)){
        $params.Add("OutputAssembly", $OutputAssembly)
    }

    if ($UseTypeAlias)
    {

        #Guid suffix to create unique class name
        $uniqueSuffix = "_{0}" -f [Guid]::NewGuid().ToString().Replace("-", "_")

        #Regex to find class declarations
        $regex = [regex] "(?<=public\s+(static\s+)?(partial\s+)?class\s+)\w+"
 
        #Replace class name to unique name
        $code = $regex.Replace($sb.ToString(), [String]::Format("{0}{1}", "$&", $uniqueSuffix))
 
        #Add replaced code definition
        Add-Type @params -TypeDefinition $code
 
        #Add Alias to original class name
        foreach ($match in $regex.Matches($code))
        {
            $className = $match.Value.Replace($uniqueSuffix, "")
            #Write-Verbose ("Set class name alias '{0}' to '{1}'" -f $className, $match.Value) -Verbose
            [PSObject].Assembly.GetType("System.Management.Automation.TypeAccelerators")::Add($className, $match.Value)
        }
    }
    else
    {
        #Add replaced code definition
        Write-Verbose "Call Add-Type with no type aliases"
        Add-Type @params -TypeDefinition $sb.ToString()
    }
}