That's only "Up to" 240/250v, it will not give you any higher voltage that what input to it is. Typical household voltage is 220v so that's all it will output. What it's supposed to do is to cut down on transient voltages that may reach much higher voltages, even in 1000's volts, in case of that one 6000v. It's not going to stop lightning strike for instance which can reach 100s of thousands volts. For most practical purposes it's just a glorified extension cord.