Digikey sources its parts from the manufacturers and adds a retail markup.
The Alibaba seller takes remnants from someone’s production run. For example, if someone orders 10000 products, which may have 3500 parts roll left over in the warehouse of the PCB factory, the PCB factory can distribute these leftover parts to other order. So, seller on Alibaba, the PCB factory, don’t pay full price for parts due to bulk purchasing. Then, the unit price is lower.
Read More: The Supply Chain Management of PCB Factory