ConvertFrom-HexString.ps1

<#
.SYNOPSIS
   Convert from Hex String
.DESCRIPTION
 
.EXAMPLE
    PS C:\>ConvertFrom-HexString "57 68 61 74 20 69 73 20 61 20 68 65 78 20 73 74 72 69 6E 67 3F"
    Convert string to hex byte string seperated by spaces.
.EXAMPLE
    PS C:\>"415343494920737472696E6720746F2068657820737472696E67" | ConvertFrom-HexString -Delimiter "" -Encoding Ascii
    Convert ASCII string to hex byte string with no seperation.
.INPUTS
    System.String
#>

function ConvertFrom-HexString {
    [CmdletBinding()]
    param (
        # Value to convert
        [Parameter(Mandatory=$true, Position=0, ValueFromPipeline=$true)]
        [string[]] $InputObject,
        # Delimiter between Hex pairs
        [Parameter (Mandatory=$false)]
        [string] $Delimiter = ' ',
        # Output raw byte array
        [Parameter (Mandatory=$false)]
        [switch] $RawBytes,
        # Encoding to use for text strings
        [Parameter (Mandatory=$false)]
        [ValidateSet('Ascii', 'UTF32', 'UTF7', 'UTF8', 'BigEndianUnicode', 'Unicode')]
        [string] $Encoding = 'Default'
    )

    process
    {
        $listBytes = New-Object object[] $InputObject.Count
        for ($iString = 0; $iString -lt $InputObject.Count; $iString++) {
            [string] $strHex = $InputObject[$iString]
            if ($strHex.Substring(2,1) -eq $Delimiter) {
                [string[]] $listHex = $strHex -split $Delimiter
            }
            else {
                [string[]] $listHex = New-Object string[] ($strHex.Length/2)
                for ($iByte = 0; $iByte -lt $strHex.Length; $iByte += 2) {
                    $listHex[[System.Math]::Truncate($iByte/2)] = $strHex.Substring($iByte, 2)
                }
            }

            [byte[]] $outBytes = New-Object byte[] $listHex.Count
            for ($iByte = 0; $iByte -lt $listHex.Count; $iByte++)
            {
                $outBytes[$iByte] = [byte]::Parse($listHex[$iByte],[System.Globalization.NumberStyles]::HexNumber)
            }

            if ($RawBytes) { $listBytes[$iString] = $outBytes }
            else {
                $outString = ([Text.Encoding]::$Encoding.GetString($outBytes))
                Write-Output $outString
            }
        }
        if ($RawBytes) {
            return $listBytes
        }
    }
}