What PSU specifically are you using?
My PSUs all have exhaust fans. Typically exhausting upward from the fan out the top of the PSU. I would agree an intake fan would appear backwards.
The brick-style server PSU's all have fans on the end and AFAIK only the HP DP-series and Dell PSU's have the air coming out the fans. All Bitmain PSU's exhaust out the 12V output end as do the Soccerer's. Not the best idea for miners but then again the PSU's put out very little heat so is mostly a moot point.
I assumed my APW3's were the same as my ATX's with an exhaust fan. Apparently I've never actually felt to see if they were intake fans.