Yahoo was using Bing from around 2010 to 2015. But since then they've been using a variety of sources - Bing, Google, and presumably their own, and I think it can mix the results.
Yahoo's search business was always odd... They had their own search, then switched to search powered by Google. Then they purchased Overture, which owned AlltheWeb and AltaVista. Overture had originally purchased AlltheWeb from FAST, who had pivoted into the enterprise space, and later got bought by Microsoft and integrated into SharePoint.
DDG actually was using Yahoo as a serach provider and now uses Yandex. The ads on DDG are from the Yahoo network.
> AOL & Yahoo is really Bing What? I don't get that -- I don't know about AOL, but I thought that Yahoo does its own crawling (their Slurp bot)
AOL has Bing in the footer, Yahoo had Bing references in the source view when I checked, although it looks like what tallanvor said and they just return mix of search engines.
They used to. That changed like 8 years ago. https://en.wikipedia.org/wiki/Yahoo!_Search
To get DDG you'll need to use a different browser like FF.
I actually blocked Chrome on my phone and started using FF once I noticed that Chrome was updating itself even though I was requiring manual updates. Play Store and Google Play Services do the same thing, but don't have a good alternative for them,