Sort of, They are called Radioisotope Thermoelectric Generator (RTG) used where you need a small amount of super reliable power. Mainly used on deep space missions where there is not enough sunlight. The soviets also used them in unmanned deep north lighthouses.
https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...
Neat tech, but very inefficient, to make it efficient fluids start needing to be moved around which hurts reliability. The next step up are pebble bed reactors, I don't think any have been built but the idea is to have self contained fuel "pebbles" enriched enough to get hot but with enough built in moderation so they can never melt down. Then a traditional heat engine is bolted on.
RTGs aren't quite the same, in that they use simple radioactive decay, no? And cooling in space is really hard.
Would this increase in performance they discovered make deep space satellites more powerful?
Not for the ones already launched and we're not launching any of those in the near future, especially not with the current batch of governments.
And I'm not convinced that particular discovery would yield that kind of performance increase for such an application. There are just too many things different in the environment alone.