Phoenix is kind of spendy. As a rough estimate,I would say a minimum of 70k approaching 100k (depending on fringe benefits such as stock options, bonuses, etc). I am not up to speed on power supply designers salary but speaking more about Sr. EE's in general. I lived in South Dakota a while back as a Sr. and was making 60K with fringe benefits. Hope this helps.
One other note is too be careful about these online pages that supposedly compare salaries amongst regions in the US to give you some idea as too how much you should make, based on your present salary, to enjoy the same lifestyle in another region. I found them to be WRONG. I checked 6 of these kinds of pages when moved from South Dakota and only 2 said I would have to make more. The other 4 said I could make less. I found I had to make more to enjoy the same life style (quite a bit more, actually). So beware.