Strange, Both have different purpose! AMOS (a component of SPSS) validates a measurement model and structural model (SEM) whereas SPSS without AMOS does common statistical calculation for data analysis. If one can establish a model with SPSS tools without AMOS, it may be skipped, though difficult I guess. AMOS is add on to base SPSS and costs extra.
Hayes, A. F., Montoya, A. K., & Rockwood, N. J. (2017). The analysis of mechanisms and their contingencies: PROCESS versus structural equation modeling. Australasian Marketing Journal (AMJ), 25(1), 76-81.