The software allows you to add multiple PST files into Outlook, but I didn't see anything related to comparison of two files. However, I've seen that they have another tool used to compare the PST files. It also displays the differences and the duplicates found in the file.
Please take a look at the following page where the app is hosted: https://www.systoolsgroup.com/email-duplicate-analyzer.html
Note: Before buying, test the software by downloading the trial.