I have successfully installed both Apps (AWCC & Support Assist) by manually download installation package from Dell's website.
However, I was not able to install both Apps from Windows Store. I tried to install them from Windows Store yesterday (May 15th), and both of them didn't work.
I am using Alienware 17 R5, and when I was trying to install them from Windows Store, the following happens:
For Support Assist, Windows Store pops a notification says something like "the laptop you are using is not supported". Which is not true, as I manually installed the App later, my laptop is clearly supported.
For Command Center, it seems Windows Store runs into some sort of error and download simply failed.
I wasn't even able to installed it using the installation package at the first time. I somehow fix this issue by "reinstall" the Command Center.
Again, I fixed both issues by manually install both Apps, however, I think it's best to report problems with Windows Store.