If you were building a new house, installing a 200 amp. It should not add more than a few hundred dollars to the cost of the wiring. A watt is voltage multiplied by amperage. A 100 watt bulb uses 110 volts and about .9 amps. A bulb manufactured for one system can't be used in the other, while most lap top computers can.
Transformers are devices which 'transform' or convert one voltage into another.
It has a section on electrical theory and lots of practical stuff too. My copy is dog eared and within arms reach of the computer. Inc. All Rights Reserved.