$Date = Get-Date -format "yyyyMMdd_HHmm"
$File = "C:TempMyFile"+$Date+".xml"

$Query = "exec dbo.usp_MyProc"

Invoke-Sqlcmd -Query $Query -database MyDatabase -ServerInstance MyServer | out-file $File -Encoding utf8

[xml]$Result = Invoke-Sqlcmd -Query $Query -database MyDatabase -ServerInstance MyServer
$Result | out-file $File -Encoding utf8

Invoke-Sqlcmd -Query $Query -database MyDatabase -ServerInstance MyServer |ConvertTo-XML |Out-File $File -Encoding utf8

function Format-XML {
  [CmdletBinding()]
  Param ([Parameter(ValueFromPipeline=$true,Mandatory=$true)][string]$xmlcontent)
  $xmldoc = New-Object -TypeName System.Xml.XmlDocument
  $xmldoc.LoadXml($xmlcontent)
  $sw = New-Object System.IO.StringWriter
  $writer = New-Object System.Xml.XmlTextwriter($sw)
  $writer.Formatting = [System.XML.Formatting]::Indented
  $xmldoc.WriteContentTo($writer)
  $sw.ToString()
}

$Date = Get-Date -format "yyyyMMdd_HHmm"
$File = "C:TempMyFile"+$Date+".xml"

$Query = "exec dbo.usp_MyProc"

Invoke-Sqlcmd -Query $Query -database MyDatabase -ServerInstance MyServer `
  | Format-XML `
  | Set-Content -Path $File -Force

$Date = Get-Date -format "yyyyMMdd_HHmm"
$File = "C:TempMyFile"+$Date+".xml"

$Query = "exec dbo.usp_MyProc"

$resultRow = Invoke-Sqlcmd -Query $Query -database MyDatabase -ServerInstance MyServer


$resultRow['XMLColumn'] | Set-Content -Path $File -Force