Nothing protects from a direct hit, its just too massive. So we need to figure out a way to lessen the possible impact summer storms will have on us. This is pretty good insurance that the device will protect you in all but the most severe cases. In severe cases the UPS will give up its life to protect the computer. There are a number of good UPS manufactures, as with all shopping compare prices and specs for the best buy.
Capacity is a somewhat arbitrary specification from the view of is it enough.
There are a lot of low cost devices on the market that give you very minimal capacity at the lowest possible cost. Buy the device with some reserve capacity. Never connect a laser printer to one of these device s as the power draw from the printer is just too great and will disable the device or cause a very large downward spike in the power output. Some of the better units have a connector for the telephone line and do a surge protection for that device before it gets to your computer. So far we have only been talking about using an UPS as a protection device.