Migrate existing dev desktop site from PC to Mac without existing db dump
DevDesktop stores the mysql databases in its application installation folder.  Assuming, you installed to the default location, in your PC backups, navigate to C:\Program Files (x86)\DevDesktop\mysql\data
This folder contains a copy of the MySQL databases.  


Restoring to PC for use or export:


On the PC (assuming you haven't installed any other devdesktop sites), copy all the files and folders from the mysql/data backup directory into a fresh install's MySQL's data directory.
For export:  Start MySQL and export a copy for backup purposes/importing elsewhere as needed.
For immediate use/development on PC: Start MySQL and your DevDesktop to confirm the site is running; resume normal dev desktop development on PC

Loading directly to a fresh install of DevDesktop, MAMP, Vagrant, or other MySQL service on Mac


You could also copy the contents of that backup folder directly to the corresponding mysql/data backup directory on your Mac.  NOTE: copying the entire directory will wipe all existing databases/user accounts in MySQL on your Mac's MySQL server, be sure to back it up first if you have existing data).  If it's a fresh install of DevDesktop (or other) on the Mac, copy all the files and folders from the mysql/data backup directory of the PC to the corresponding folder on the Mac.
Start DevDesktop or other local webserver app to confirm the site is running; resume normal dev desktop development on Mac

Merging with existing mySQL data, hosting database along side others on existing install of DevDesktop, MAMP, Vagrant, or other mySQL service on Mac


If you do have existing MySQL data on the Mac (be it MAMP, DevDesktop, Vagrant instance or other), backup the corresponding /mysql/data folder from that application.  
Replace with the backup folder from the PC
Start MySQL and export the database.
Then swap the original Mac MySQL data back into place.
Restart MySQL and import the database backup you just exported.  
Now you have both your PC devDesktop database and Mac databases available on the Mac.