A colloquialism used to describe the type of external power supply where the transformer, and sometimes other components, are located in a box that houses the connector that plugs into the electrical outlet. These types of power supplies have seen wide spread use in the last ten or so years due to their low cost, ease of manufacture, versatility, and sonic improvements; equipment with external power supplies are usually quieter (all other things being equal) than equipment with internal supplies. A company who builds many devices which do not require a lot of power to operate may be able to use one generic power supply for each of them, which greatly reduces the cost of the development for each device. Since only the device which connects to a wall outlet must be UL approved (see WFTD archive UL), each new device that a manufacturer develops does not have to go through the time and expense of getting UL approval.
Many consumers do not like these types of power supplies, however, because the size and weight of the box that plugs into the electrical outlet can be cumbersome. They are large enough that one of these supplies usually will cover two or more outlets on a typical power strip, and heavy enough that when plugged in to a wall (or vertically positioned power strip) they can fall out very easily. Many manufacturers are now aware of the public’s disdain for wall warts and have been making more of an effort to include the power supply inside of their equipment, which allows a standard power cord to be used. If cost or other factors do not allow for internal power supplies manufacturers have been leaning towards “lump-in-the-line” supplies, where the transformer box is half way between the electrical plug and the connector to the equipment. This solves most of the problems of external power supplies while retaining most of the advantages of them.