Google is testing an interesting PLA carousel.  This one will break down a more generic product search to show groups of items split up by retailer.  It seems to show up when a searcher is searching for something that is a bit more generic, and would need to be targeted a bit tighter to show the best – and most accurate – shopping ads.

They offer mini selections within the product listing ads to narrow it down by either retailer, both offline retailers and online ones and brands.

Here is what it looks like:

And another look when you further scroll through the carousel:

This allows Google to do a bit better targeting with their PLAs when someone does a more generic product search, to help them narrow down the product they are looking for.  Then Google can show more targeting shopping ads based on the user selection.

Google AdWords could also use the selections users make to help target their PLAs for more generic product searches in the future.