Equivalent to C#’s “using” keyword in powershell?

There’s really nothing at the namespace level like that. I often assign commonly used types to variables and then instantiate them:

$thingtype = [FooCompany.Bar.Qux.Assembly.With.Ridiculous.Long.Namespace.I.Really.Mean.It.Thingamabob];
$blurb = New-Object $thingtype.FullName

Probably not worth it if the type won’t be used repeatedly, but I believe it’s the best you can do.