Can't mount any dmg El Capitain

Help! I just started having an issue where I can't mount any DMG files on my Macbook Pro! I recently upgraded to El Capitain and everything seemed to be find until today. Here's what I noticed, which may or may not have had an impact.

I plugged in my iPad using a cheap third party lightning cable from Target which barely works in the wall and I got a prompt saying "USB devices disabled. Unplug device consuming too much power to enable." I unplugged the iPad and the cheap cable then went to mount the Android Studio DMG file I just downloaded. I got the "no mountable filesystems" error. I tried to download the dmg again but the problem persisted. I then tried to download a few other DMG files as I suspected there was actually nothing wrong with the Android Studio DMG. I tried the SourceTree dmg as well as Charles Proxy's dmg and they all give the same error. I tried to reboot and I still have the problem. I suspect I may have damaged something with this cheap USB cable but I'm not sure. Is there a way to identify/fix the problem here? It just started happening today immediately after I tried the cheap cable.

I'm also seeing this error when I open the Mac App store and click the updates tab:

The operation couldn’t be completed. (NSURLErrorDomain error -1012.)