On upgrading yesterday to El Capitan I found my USA-28XG was no longer recognized. It had been working under Yosemite via the last driver specifically named for it ("Driver for USA-28XG_v2.6.4 (Mac OS X 10.6.x to 10.8.x).zip" on the Tripp Lite site).
I tried several things that didn't help, then on a hunch downloaded their more recent file "USA-49WG-v1-and-v2-Mac-Drivers.zip" that would appear to be specific for the four port converter, but it's not :-)
The installer notes that the driver in the enclosed package named "Keyspan Serial Adapter Driver_v4_Mac OS X 10.9_10.10.pkg" will work with many different devices - specifically:
One Port DB9: USA-19HS, USA-19, USA-19Qi, USA-19W, USA-19QW
Two Port DB9: USA-29WG
Two Port Din8: USA-28XG, USA-28X, USA-28
Four Port: USA-49WG1, USA-49WG, USA-49W, USA-49WLC, USA-4E230
Other: USA-18X, UPR-112, UPR-112G
So I deleted the old driver (using Keyspan Serial Assistant) and ran the installer on my El Capitan system. And it failed with a not very helpful error message. But then I tried a custom install of only the KeyspanUSAdriver, unchecking the USAdriverFolder. This operation completed and I found the driver in Library/Extensions/ (not System/Library/Extensions where the previous driver had been). System Information:Extensions (opened through About This Mac; System Report) indicated that the driver had been found but not loaded.
I restarted the computer, to see if the driver would become loaded, but it was not... My serial adapter had been unplugged throughout all of this, so I decided to plug it in - and this crashed the computer! But when it rebooted everything worked! I have not restarted since, and will try that soon to verify that there are no ongoing issues. If there are I'll report back.
So, to more specifically answer your question - I think you can likely use the 10.9 - 10.10 driver I mentioned above for your USA-19HS. It may install without you having to resort to the custom install that I tried if you install before upgrading to El Capitan. I would try this more traditional route before turning to command line tricks.