Change a local user account's password using PowerShell

Set-LocalAccountPassword.ps1

$Username = "su"
$Password = "password"

$adsi = [ADSI]"WinNT://$env:COMPUTERNAME"
$existing = $adsi.Children | where {$_.SchemaClassName -eq 'user' -and $_.Name -eq $Username }

if ($existing -eq $null) {
    Write-Error "User $Username does not exist"
    return
}

$existing.SetPassword($Password)