I have just done a clean install of Windows 10 on my Dell Inspiron 15R-7520 and the USB card reader was not working. When i checked Device Manager it showed a device listed as USB2.0-CRW was not installed. Windows was unable to find a suitable driver so i installed "Dell SupportAssist for PCs and Tablets" from http://www.dell.com/support/contents...support-center.
I then ran Dell SupportAssist and on its startup window/home page the Drivers and Downloads tile showed an update was available for Realtek USB Card Reader so i installed it and the USB card reader is now working.
NB. when you start Dell SupportAssist it does a scan of your system so you have to wait a minute or 2 before all items/info are available on its startup page.