Set startup account of a Scheduled job in PowerShell. See https://stackoverflow.com/questions/40569045/register-scheduledjob-as-the-system-account-without-having-to-pass-in-credentia/60554216#60554216

Register-ScheduledJob-under-the-system-account.ps1

# For https://stackoverflow.com/questions/40569045/register-scheduledjob-as-the-system-account-without-having-to-pass-in-credentia/60554216#60554216

$ErrorActionPreference = 'Stop'
Clear-Host

#### Start of Main Logic ###########################

$taskName = "my_PowerShell_job"

$accountId = "NT AUTHORITY\SYSTEM";
#$accountId = "NT AUTHORITY\LOCAL SERVICE";

$task = Get-ScheduledJob -Name $taskName  -ErrorAction SilentlyContinue
if ($task -ne $null)
{
    Unregister-ScheduledJob $task  -Confirm:$false
    Write-Host " @ The old ""$taskName"" PowerShell job has been unregistered"; Write-Host;
}

# Uncomment the following exit command to only delete your job.
# exit;

# Shchedule your job. Using of -AtStartup as an example.
$trigger = New-JobTrigger -AtStartup;

$options = New-ScheduledJobOption -StartIfOnBattery  -RunElevated;

Write-Host " @ Registering of ""$taskName"" job";
Register-ScheduledJob -Name $taskName  -Trigger $trigger  -ScheduledJobOption $options `
    -ScriptBlock {
		# Put your code here.
        Write-Host Your job has been launched!;
    }


$principal = New-ScheduledTaskPrincipal -UserID $accountId `
    -LogonType ServiceAccount  -RunLevel Highest;

$psJobsPathInScheduler = "\Microsoft\Windows\PowerShell\ScheduledJobs";
$someResult = Set-ScheduledTask -TaskPath $psJobsPathInScheduler `
    -TaskName $taskName  -Principal $principal

#### End of Main Logic ###########################

Write-Host;
Write-Host " @ Let's look at running account of ""$taskName"" PowerShell job"
$task = Get-ScheduledTask -TaskName $taskName
$task.Principal

Write-Host " @ Let's start ""$taskName"" manually"
Start-Job -DefinitionName $taskName | Format-Table

Write-Host " @ Let's proof that ""$taskName"" PowerShell job has been launched"; Write-Host;
Start-Sleep -Seconds 3
Receive-Job -Name $taskName
Write-Host;