I realized I hadn't been making this clear enough: power rating improves the base damage of all your abilities.
What does this mean for critical hits? Power rating increases the base damage that critical hit calculations (with surge) take into account. Power basically makes all of your damage better across the board. However, you hit massive diminishing returns when you attempt to stack stats in any way on your gear.
How is this applicable to Sniper? Well, I don't recommend stacking stats at any point, but I do love temporarily stacking power rating (relic + adrenal) in order to do massive amounts of normal and crit damage. What stims and adrenals allow you to do is get very close to the power cap. At that point, your crit/surge ratings come into play (scaled off your new base damage) and you end up hitting like an absolute truck.
Basically you want to use the Field Tech gear that BWA has designed for you and stack power rating from consumables and relics on top of that.
How does it work in practice? Ask the people I just triple-killed with Orbital Strike.