after-tax employee contributions more than 1 plan

If an individual was in 2 different retirement plans, both of which permitted after-tax employee contribution, could the individual contribute say $50,000 after-tax into each (assuming compensation is high enough, passes testing, etc)?

Unrelated employers?   Basically the annual additions limit rules will come into play. 

When evaluating whether there are related employers, keep in mind the reduced ownership threshold for controlled groups under 415(h) and the special rule for 403(b) plans under 415(k)(4).