TFS Build: `Microsoft.TeamFoundation.PowerShell' is not installed on this computer
I had this issue and to solve I notice that by default the cmdlets are not added during the PowerTools installation. You need to run a full install to make it work.
I posted here some pictures: https://fabiostawinski.wordpress.com/2016/07/11/the-windows-powershell-snap-in-microsoft-teamfoundation-powershell-is-not-installed-on-this-computer/
I am going to have a quick punt here and say it is probably something to do with 32-bit vs 64-bit powershell. If I run Add-PSSnapinicrosoft.TeamFoundation.PowerShell from normal 64-bit powershell fine. But if I run it from C:\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell_ise.exe I get the above exception. I am going to go ahead and say that the build server is a 32-bit application and there for starting a 32-bit runtime.
Not really sure what the fix is exactly but maybe the following will point you in the right direction.
PowerShell (2.0, 32-bit) can't load TFS 2010 snap-in... except when it can
For me it was another issue because I was trying to use Power Tools with only Visual Studio 2017 Pro installed.
For Visual Studio 2017 they didn't released Microsoft Team Foundation Server 2017 Power Tools. They are saying that the previous version it should work with any higher version of Visual Studio that has TFS.
The problem is that if you have only Visual Studio 2017 installed you will not be able to install Microsoft Team Foundation Server 2015 Power Tools for example, because having Visual Studio 2015 (any version) installed is a requirement for installing Microsoft Team Foundation Server 2015 Power Tools.
In other words I had to install Visual Sudio 2015 then install Microsoft Team Foundation Server 2015 Power Tools and then Add-PSSnapin Microsoft.TeamFoundation.PowerShell worked.
Please refer also to this:https://developercommunity.visualstudio.com/content/problem/103642/team-foundation-server-2015-power-tools-install-is.html
Hopefully this would help somebody.