MIL-STD-704A, Curve 1 for +28V power, represent voltage transients that can appear on a 28VDC line. You can burn dollars to buy simulators that will reproduce that DC level and those transients, but if you just want to beat up your prototype(s) for a while, you can use an inexpensive test fixture as shown below to loosely mimic those DC plus transients combinations.

20170618_EDNA_NT01_01 Figure 1: Illustration of a MIL-STD-704 simulator.

When being used to mimic a MIL-STD-704 situation, a +28V DC input goes to the input labelled DC IN which is the anode of the 1N1204. A higher voltage supply of up to 80V DC goes to the input labelled Hi-V IN. The pin labeled DC OUT then carries +28V DC less the 1N1204 voltage drop but punctuated by eighty volt transients in keeping with the timing set by the ICM7155.

An operating setup would look like the following sketch.

20170618_EDNA_NT01_02 Figure 2: The operating setup.