There's A LOT of MISINFORMATION on this thread.
Powerline adapters do not need to be on the same circuit breaker, they need to be on the same PANEL/Meter and on the same pole(bus bar) of the panel. But certainly, they never needed to be on the same circuit breaker. Powerline adapters can even work through a sub-panel, as long as it connects to the original panel in the home. I have powerline adapters working through my house to a sub panel in my detached garage. Even the old actiontec AV500 I had works to my garage.
So generally speaking, with a typical 2 phase 120/240v household, you have a 1 in 2 chance that the power line adapter with work between circuit breakers. If the circuit breakers are on the same bus bar, it will work. Now if you have a specific location to place your powerline adapter, you can simply move the circuit breaker to the same bus bar as the other outlet so they're on the same bus bar. It's not that hard.
You can see in the picture below, as long as both outlets are on the same black or blue bus bar, then they're on the same node and will work. They'll even work through a sub panel as shown, as long as both outlets and breakers are on the same bus bar.