I've created a pssession on a remote computer and entered that possession. From within that session I use start-process to start notepad. I can confirm that notepad is running with the get-process command, and also with taskmgr in the remote computer. However, the GUI side of the process isn't showing. This is the sequence I've been using:
$server = New-PSSession -ComputerName myserver -Credential mycreds
Enter-PSSession $server
[$server]: PS C:\>Start-Process notepad -Wait -WindowStyle Maximized
The process is running, but while RDP'd to the box, notepad does not open. If I open notepad from the server, a new notepad process begins. I also tried by using the verb parameter like this:
[$server]: PS C:\>Start-Process notepad -Wait -WindowStyle Maximized -Verb Open
Same result tho... Process starts, but no notepad shows. I've tried this while remoted into the box (but issued from my local host) as well as before remoting into the server.
That is because your powershell session on the remote machine does not go to any visible desktop, but to an invisible system desktop. The receiving end of your powershell remote session is a Windows service. The process is started, but nor you nor anyone else can ever see it.
And if you think about it, since multiple users could RDP to the same machine, there is really no reason to assume a remote powershell session would end up showing on any of the users desktops. Actually, in almost all cases you wouldn't want it anyway.
psexec with the -i parameter is able to do what you want, but you have to specify which of the sessions (users) you want it to show up in.