The Shure PS24US is a replacement power supply for Shure your SLX4, PGX4, or BLX4 wireless receiver. (The PS24US is the replacement model for the PS23US power supply.)

NOTE: In order to cut consumer utility costs and set higher standards of energy efficiency, the U.S. Department of Energy implemented a mandate that all external AC adapters be "Level 6 energy compliant." To comply, Shure has updated its power supplies and chargers from level 5 to level 6 energy efficiency, which is why the 24 replaced the 23.  Other than that, they are the same.

You will receive one or the other, as we have a mixed bag.