The first thing to check are the coordinate systems (projections) of the source data and your target system.
AddXY gives positions relevent to the coordinate system: lat/long if the data is in geographic, some measured unit (meters or feet for example) in a projected system.
Note that the x,y coordinates are based on the input's coordinate system, not that of the ArcMap data frame.
If the source and target systems are different, the locations can be quite funky.