PSDX files are used by Photoshop Touch version for tablets. You do not need to convert psd to psdx to open in Photoshop Touch.
Upload your PSD file on your desktop to the Creative Cloud. Then on your Photoshop Touch, click New From -> Creative Cloud. From there you can open up psd files on your tablet directly.
However, the layers in your original psd files will be flattened.
It should be quite possible to simply re-save PSD format to PSDX with Adobe Photoshop CC. But PSDX files must be smaller and easier to read due to mobile phones and tablets performance.