It looks like Yahoo is making adjustments to their maladjusted prices. This was a recent sample for XRX a few days ago: [...] Date Open High Low Close AdjClose Volume 20/06/17 28,73 28,88 28,31 28,33 28,09 2443700 19/06/17 28,72 28,99 28,54 28,79 28,54 3163700 16/06/17 27,88 28,84 27,84 28,50 28,25 7246700 15/06/17 27,43 28,14 27,18 27,79 27,55 3518800 14/06/17 28,04 28,16 27,44 6,93 27,48 1520900 13/06/17 28,28 28,44 28,00 7,01 27,80 960800 12/06/17 27,76 28,60 27,76 7,06 28,00 1608300 09/06/17 27,72 28,16 27,60 6,94 27,52 1333400 08/06/17 28,16 28,16 27,80 7,00 27,76 1584700 07/06/17 28,00 28,20 27,60 7,04 27,92 2134200 [...] Today: [...] Date Open High Low Close AdjClose Volume 20/06/17 28,73 28,88 28,31 28,09 28,33 2443700 19/06/17 28,72 28,99 28,54 28,54 28,79 3163700 16/06/17 27,88 28,84 27,84 28,25 28,50 7246700 15/06/17 27,43 28,14 27,18 27,55 27,79 3518800 14/06/17 28,04 28,16 27,44 27,48 27,72 1520900 13/06/17 28,28 28,44 28,00 27,80 28,04 960800 12/06/17 27,76 28,60 27,76 28,00 28,24 1608300 09/06/17 27,72 28,16 27,60 27,52 27,76 1333400 08/06/17 28,16 28,16 27,80 27,76 28,00 1584700 07/06/17 28,00 28,20 27,60 27,92 28,16 2134200 [...] Seems like OHL and AdjClose are now adjusted for splits and dividends. The adjusted close is within the limits of high/low, back to 1977. The unadjusted close is adjusted for splits but not for dividends, apparently. Obviously everything is very different from other sources such as Quandl. This is the oldest sample for XRX from Quandl: [...] Date Open High Low AdjClose Volume 13/07/87 25,11 25,27 24,82 24,86 3407850 10/07/87 25,31 25,35 25,11 25,31 2076750 09/07/87 25,31 25,48 25,19 25,35 1269900 08/07/87 25,48 25,56 25,27 25,31 1838250 07/07/87 25,35 25,56 25,35 25,48 889200 06/07/87 25,73 25,73 25,35 25,4 1252800 From Yahoo: [...] Date Open High Low Close AdjClose Volume 13/07/87 33,32 33,54 32,94 32,99 1724300 10/07/87 33,60 33,65 33,32 33,60 1050800 09/07/87 33,60 33,82 33,43 33,65 642500 08/07/87 33,82 33,93 33,54 33,60 930100 07/07/87 33,65 33,93 33,65 33,82 449900 06/07/87 34,15 34,15 33,65 33,71 633900 All of this just for XRX, still too early to draw conclusions, but nonetheless encouraging.
It looks like Yahoo is back to normal after the Verizon takeover. The downloader that I use, HSQuote, had to be modified in order to handle Yahoo's new format. Other downloaders that I know of also had to be modified. Since Verizon took over it appears that problems posted on Yahoo's help forum actually get addressed. I might mention that during the problem period I tried Google and the data was OK but the speed was much slower than Yahoo.
In addition to the data suppliers that you list, there is a new "kid" on the block that might be worth looking into: https://www.tiingo.com/
I used MLDownloader for a long time and they provided adjustments as needed when something changed at Yahoo. Then that stopped although it is still for sale but without support I would not go down that road.
I have it but I didn't use it often. When yahoo changed things I tested and confirmed that it was not working. I was wondering if now would become good again, changing any url or something like that.
Latest version of Amiquote from http://amibroker.com/products.html will download free eod, historical eod and intraday data from tiingo, google, stooq, quandl and finam as well as yahoo. So I guess you could maintain multiple databases on your PC.
I use several programs the accept Metastock format. The problem with AmiQuote is that it does not convert and store Metastock data. AmiBroker will accept Metastock but one has to either use a downloader that saves data in Metastock format or write and run a program that will convert AmiQuote data. When one needs Metastock format it is much easier to use a downloader that automatically stores data in that format.