Windows – using powershell to update system path doesn’t immediately work

I am trying to use powershell to update Windows system path by :

$oldpath = (Get-ItemProperty -Path ‘Registry::HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment’ -Name PATH).path
$newpath = "$oldpath;C:\nuget"
Write-Output "PATH:$newpath"
Set-ItemProperty -Path 'Registry::HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment' -Name PATH -Value $newPath -Force
Get-ItemProperty -Path ‘Registry::HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment’ -Name PATH   

it seems work, Get-ItemProperty does show "C:\nuget" is added into path. The problem is then i start a new powershell console or a command line console, and type "nuget", I still get "The term 'nuget' is not recognized as the name of a cmdlet, function, script file, or operable program"

in the new powershell console, if I rerun Get-ItemProperty, it shows the new Path is there, it's just doesn't immediately take effect in current user session. If I run "set " in cmd console, the new Path wasn't there in PATH variable.

BTW, after Set-ItemProperty was run, I checked control pannel->System->Advanced system setting->Environment Variables, the new Path I added is there.

I found if I manually modify the Path through Windows system setting, it will take effect immediately ( new cmd/powershell will have it); but if the path is modified by powershell Set-ItemProperty command, then I have to logoff, then login, then new Path will take effect.

Feels like the system Path is cached in the current user login session.