The Dell is neither I would expect that work. But it may have some Dell quirk.
115200 is the correct baud rate. If you're the serial console though you will need to boot from the USB image:
https://nyifiles.pfsense.org/mirror/downloads/pfSense-CE-memstick-serial-2.4.3-RELEASE-amd64.img.gz
Or set the console at boot:
https://www.netgate.com/docs/pfsense/hardware/boot-troubleshooting.html#booting-with-an-alternate-console
Steve