Do you need power bash for this purpose? I haven't taken the power bash perk yet, but my regular bash seems to do a good job of interrupt/stagger.
Shield bash works well enough that you don't really need power bash (In my opinion). I personally prefer the regular shield bash over power bash because it's far quicker which means that there are far more situations where you can use it without taking damage. Because a power bash is fairly slow and roots you during it's duration, often times you will either miss a moving target or get hit in the process.
Also, you can make a regular shield bash act like a normal power bash if you time it right after blocking an enemies attack (Shields only because with a weapon you're not capable of bashing immediately after blocking a hit. Keep in mind that the timing is crucial and it may not be easy for some.). And like I said in my other post, when you meditate on the word Fus, the difference between a shield bash stagger and a shield power bash stagger is negligible.