eXch.net is down, yes. It's no longer working. exch.cx redirected to eXch.net but is now redirecting to exch.pw as you noticed. exch.pw is legit. It's eXch's domain. Check the OP of this thread. You will see exch.pw being mentioned as the current active domain. However, if you are thinking of swapping some funds, I recommend that you do it over TOR and using the official .onion domain. It's better for your privacy. Plus, exch.pw seems quite slow at the moment.