It's a power cable adapter.
Great price. Eliminates lots of clutter when using SATA drive with older power supply. With both plugs combined it stays connected to drive better as well.
Good approach to convert older PC power supplies to power SATA HDD. Better fit using this than seperate power and data cables.
MCM has a tremendous selection of products that make my job easier to perform. Along with great pricing and fast shipping, I enjoy ordering and using their products.