I use a $10 smartcard reader, the SCR 3500 [info - http://www.scm-pc-card.de/index.php?lang=en&page=product&function=show_product&product_id=637 , amazon - http://amzn.to/1Hf0Srm ] . Portable, compact, and cheap. But not officially supported by our internal Microsoft IT team. I've been using the SCR3500 from Windows 7 through Windows 8.1 .
So I upgraded my HP810 to Win10 Build 10076 at the office. All good so far. I was using a ethernet cable during the upgrade for PXE boot upgrade. Very nice experience.
Next it was time to get onto the wifi in my office, as well as get setup for remote access to our corpnet. To access our wifi, II need a smart card. So I plugged in my trusty SCR-3500 Smart Card Reader, which has never given me an issue in the past. Woops it didn't work. Ooooh, its too late for this AND the Stanley Cup is on. With Win7 and Win8 I had no issues with the SCM-3500. I would plug in the SCR 3500, the reader was recognized, drivers installed, and itsimply worked.
Now, this is the only smart card reader I had. And JimmyC wasn't in the office with his "secret mystery box" of adapters and gizmos to borrow from.
I needed the smartcard so I could install a virtual smartcard on my machine ( https://msdn.microsoft.com/en-us/library/windows/apps/xaml/dn456355.aspx ).
The virtual smart card install adds the certificates I need to get onto the intranet wireless at the Microsoft office. So without physical smart card reader, I'm not getting onto the wifi and I cannot remote into Microsoft corpnet to get to all that super secret stuff you know we have (somewhere) on our intranet!
Surfed over to the website and found the SCR 3500 is "end of life", replaced by the SCR 2910 [ http://www.scm-pc-card.de/index.php?page=product&function=show_product&lang=en&category_id=46&product_id=868 ]. Can't quite figure out where to buy a SCR2910 in the USA, but…
Long and short of it, naviagate to the SCR-3500 downloads page at http://www.scm-pc-card.de/index.php?page=download&function=show_downloads&lang=en&product_id=637 . Install the Windows 8 drivers for the SCM-3500. Voila, the smartcard reader is now recognized. Reboot may be required if you've tried adding the SCM-3500 since you last booted and it was unrecognized.
Moral of the story. Some devices that were automatically recognized on Windows 8.1 / Windows 7 may not be automatically recognized on Windows 10. Go hunt down the appropriate drivers for Windows 8. Manually install the drivers. Hopefully you get a happy result as I did.