$ErrorActionPreference = 'Stop'

# Temp. file for testing.
$f = 'tmp.txt'

$ohtParams = @{  }, @{ Encoding = 'Default' }

# Choose the non-ASCII test character.
# U+00F6 = "ö"
#  * ASCII-encoding bytes:                      0x3f (which is actually "?", which any non-ASCII char. gets transliterated to)
#  * ANSI-encoding bytes (e.g., Windows-1252):  0xf6 - single byte with high bit set
#  * UTF-8-encoding bytes:                      0xc3 0xb6  - 2-byte sequence
# Note that it is purposely not included as a literal in this
# file so as to eliminate source-code encoding issues.
$testChar = [char] 0xf6

'Set-Content', 'Add-Content' | % {

  $cmdlet = $_

  $ohtParams | % {
    if (test-path $f) { Remove-Item -Path $f -EA stop }
    $testChar | & $cmdlet -LiteralPath $f -NoNewline @_ 
    $bytes = Get-Content -Encoding Byte -LiteralPath $f
    Write-Verbose "Bytes read: $bytes"
    $actualEncoding = if ($bytes.Count -eq 1) {
      if ($bytes[0] -eq 0x3f) { 
        'ASCII'
      } else { 
        'ANSI'
      }
    } else {
      if ($bytes[0] -eq 0xc3 -and $bytes[1] -eq 0xb6) { 
        'UTF8' 
      } else {
        'UNKNOWN'
      }
    }
    [pscustomobject] @{ Cmdlet = $cmdlet; RequestedEncoding = $_.Encoding; ActualEncoding = $actualEncoding }
  }

}

Remove-Item $f