Product review (5 stars): I wish I had bought this before the expensive OEM Starter relay / capacitor
Like others have said, this works great and got my 10 year old Kenmore side by side working again.  The symptom was that instead of the compressor starting, it made a buzzing noise for a few seconds and then the overload clicks and it goes quiet.  This happens over and over every 5 minutes or so.  I noticed this a few months ago, but didn't pay much attention to it because it did eventually start and the fridge stayed cold.  When it quit altogether, I bought an expensive OEM starter relay + capacitor (plus super expensive overnight shipping) and installed them.  That seemed to help, but less than a week later, it was dead again.

Installing the Supco kit was almost as easy as the OEM part.  The instructions are clear and it comes with everything you need.  I've only had it installed for a few days, but my fridge starts every time, runs quiet and stays cold.  I know the compressor is partly worn out, so there is no way to know how long this will last.  I did a lot of research and it seems most people get another few years, though there were some accounts of many years.  In any case, it's a simple, inexpensive way to delay having to replace an expensive appliance.

For those confused about which model to get, the 400 series are for full size refrigerators / freezers and the 800 series are for smaller units.