Write some PowerShell code in any Emacs buffer.
Select it, then
M-x eval-region-powershell to evaluate as a PowerShell script block. The output goes into
*Shell Command Output*.
Update: Much improved thanks to a comment by TarMil
(defun eval-region-powershell () (interactive) (shell-command (concat "powershell -noprofile -encodedcommand " (base64-encode-string (encode-coding-string (buffer-substring (mark) (point)) 'utf-16le)))))