Russ, this only means быть во власти. The other one is TO BE EMPOWERED (to do something)

https://www.maciverinstitute.com/2018/02/new-john-doe-judge-wants-to-know-what-hes-empowered-to-do/

When a judge has a power to prescribe a sentence... would you call it 'власть'? To me, it is more like 'полномочия'. No?

When a judge has THE power to pronounce a sentence, he’s EMPOWERED to do so. We use IN POWER when we talk about governments, elected officials, rulers, presidents, monarchs, etc.

Here are examples in books of how IN POWER is used: https://www.google.com/search?tbm=bks&sxsrf=ALeKk01aokkeLwz_Yrqc1ejOK5zJ4_YTpA%3A1588022002848&ei=8kqnXsGfM8GUtQXX1KbYBA&q=%22was+in+power+at+the+time%22&oq=%22was+in+power+at+the+time%22&gs_l=psy-ab.3...31659.32801.0.32979.12.9.0.0.0.0.252.942.0j3j2.5.0....0...1c.1.64.psy-ab..12.0.0....0.951lOohAvkQ

So быть во власти is correct, but the other one isn’t.