I'm searching a way to update a Windows Universal App without the Store, so i can provide the appxbundle file from my own server. I can download this package from within the app, but i have not found a solution for installing it. The device portal core API allows only the Installation of apps, but not updating. So is there a way I can start the updating process from within my app's code?
You can package your app for Web Install, which works very similarly to Click Once for classic desktop apps. This involves pointing the user to a link with ms-appinstaller: protocol which will launch the app installer and install the package. You define the .appinstall file which contains a standardized description of the components of the app, the location of potential updates, and specifies an update policy. Automated update are described in depth in this blog post.
In addition to web install, you can apparently update the app using PackageManager. See this blog post for details.