Add-Content "C:dotnet-helpersDummyfiletoDelete.txt" "This is the last line"
# 1st create file with lines to be placed on top and then
Add-Content -Path "<path_of_file_with_top_lines_temp>" -Value (Get-Content "<path_of_original_file")
# content is in temp file
Move-Item -Path "<path_of_file_with_top_lines_temp>" -Destination "<path_of_original_file" -Force