$farm = Get-SPFarm
$file = $farm.Solutions.Item("branding.wsp").SolutionFile
$file.SaveAs("D:\FolderName\branding.wsp")
It will download Solution from SharePoint farm Solution gallary.
$file = $farm.Solutions.Item("branding.wsp").SolutionFile
$file.SaveAs("D:\FolderName\branding.wsp")
It will download Solution from SharePoint farm Solution gallary.