In powershell, I’ve seen multiple ways to stop a service

The more modern way

And the more legacy way

The legacy way is much more difficult to automate because it is not natively idempotent.

I have powershell scripts that builds a windows golden images using packer. Initially the scripts used NET STOP. I found once I switched to Stop-Service, I seemed to get more frequent failures when rebooting a VM after installing windows updates.

Do both Stop-Service and NET STOP produce the same result? Or are there differences between them that might explain why the legacy one seems more reliable?

For a Windows service that is:

• currently running
• and stoppable in principle

both net stop and Stop-Service should act the same, namely synchronously:

That is, they send the specified service a stop request and wait for stopping to complete (net stop invariably waits, while, in PSv5+, you can opt out of waiting with Stop-Service‘s -NoWait switch).

Unlike net stop (which reports an error if the service is already stopped), Stop-Service is idempotent (exhibits desired-state logic): If the target service is already in the stopped state, the command is a quiet no-op.

(As an aside: Start-Service is also synchronous, but invariably so, and is also idempotent.)

Set-Service -Status Stopped should act the same as Stop-Service, except that:

• unlike Stop-Service, it doesn’t support -Force in order to stop a service with running dependents (other services that depend on the service being stopped).
• due to what I presume to be a bug you cannot even stop services that themselves depend on other services(!).
• in effect, as of Windows PowerShell v5.1 / PowerShell Core v6.0-rc, you can only stop services with Set-Service -Status Stopped that have no dependents (no services that depend on them), nor themselves depend on other services.

Optional reading: looking at the Stop-Service and Start-Service source code:

The publicly available source code on GitHub is for the cross-platform Core edition of PowerShell, but it looks like the code in question was essentially taken unmodified from the Windows PowerShell version.

• Stop-Service: The part where the code waits for the service to be in the ServiceControllerStatus.Stopped state^[1]
  , which is only bypassed if the -NoWait switch is explicitly specified, in which case variable waitForServiceToStop is set to false.
• Start-Service: The part where the code invariably waits for the service to be in the ServiceControllerStatus.Running state.

^{[1] If reaching the target state takes longer than 2 seconds, the waiting loop issues a warning (every 2 seconds) while continuing to wait; waiting is only aborted with an error if the service is unexpectedly neither in the target-state-pending state nor in the target state.}