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).
Mac OS X driver for the Keyspan family of USB serial adapters. Mac OS X driver for the Keyspan family of USB serial adapters. Updated firmware for USA-19HS and UPR-112G (serial port). Keyspan products provide elegantly simple solutions for difficult problems, whether you need to control your presentation from across the auditorium, turn up the music from another room or use an essential serial device on a computer or laptop without a serial port. In my case, I was looking for a driver for the Keyspan USA-19QW USB to Serial adapter. It appears that Tripplite bought the company, but doesn’t seem to have the link to the driver on their website. They had a site where you could still download the driver for the Keyspan USA-19QW and other devices, but it’s been down for a few years. Keyspan USB Serial Adapter:This 'High Speed' USB Serial Adapter supports data rates up to 230 Kbps twice the speed of a standard PC serial port. Best Video Software for the Mac How To Run. Official Keyspan USA-19Qi Free Driver Download for Mac OSX. World's most popular driver download 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.
Keyspan Usa-28x B Driver Mac
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.