Hydraulic power steering fluid is really nothing special at all.
Neither is the fluid in hydraulic jacks... it's all the same stuff (basic, plain mineral oil)
ATF is usually cheaper and works as well in both situations.
NOTE: hydraulic fluid that lubricates final drives has EP additives....
it is VERY different than "plain" hydraulic fluid.
"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."