Q: What does an "offline UPS" do? A: It means the power converter stays off most of the time, until it's needed. Q: What does an "off-line power supply" do? It means the power converter stays off most of the time, right? A: No, it means it stays on as long as you have AC mains power. It's called a "off-line power supply" because it takes power *off* the AC line. English be like.