Abstract: An improved power supply adapter is provided for plug-in connection to a standard AC power supply receptacle, and to provide a DC voltage to an associated electronic instrument. The power supply adapter comprises a relatively compact case having an end face with a plurality of conductive prongs protruding therefrom for plug-in connection to an AC receptacle, such as one socket of a standard duplex or quad wall outlet or the like. An AC adapter assembly is mounted within the adapter case with the components of the AC adapter assembly arranged generally in-line between the conductive prongs and a power cord adapted for connection to the associated electronic instrument. This in-line geometry permits the adapter case to have a relatively narrow width and low profile height conforming with a single electrical socket, whereby plug-in connection of the adapter to an electrical socket does not obstruct access to adjacent sockets.