World War II at the beginning of the war having the carrier absolutely, unequivocally wins the war.
You don't even need to fire a shot, or launch a jet. On that carrier are likely hundreds or thousands of immediately usable general-purpose laptops and other computers.
Each of these computers is a super-weapon in 1939. Putting these into the hands of scientists designing planes, tanks, nuclear weapons, etc. would fundamentally transform the world, not just the war.
I bet a lot of the crew has an interest in military toys, history, etc. Maybe there are some copies of AutoCAD, Code Aster, Mathematica, PGP, etc. that would also change the world.
The economic growth change would be unparalleled. The entertainment software found on the laptops could probably fund a huge chunk of the war.
The information on radar alone would likely be enough to win the war - even if none of it existing on any computer or radar hardware on the ship. Enough crew would know enough radar, its value to the war, etc. to bootstrap radar stations quickly. The could even analyze the cavity magnetron from a microwave oven in the kitchen to jumpstart radar.
Some post WWII scenarios, same thing, but the impact continues to lessen. Korean war for example, same thing but the radar no longer is game changer. You no longer have essentially the only computers, but yours are still incomparable. Most of the rest in unchanged.
Eventually, not so much. Good to have, Mathmatica, etc. are still breakthroughs, but the existing computing infrastructure is good enough that is no longer domination time. Maybe 1990 or so.
Plenty of other goodies too. Like a pair of nice modern nuclear reactors. Desalination plant. Actual advanced radar systems. Advanced missiles. Helicopters. Kevlar armor. All ripe for using as is and/or reverse engineering.
Sure, the electronics are incomprehensible and not able to be produced soon. But sometimes knowing it is possible and just having a vague idea of what works means another scientific breakthrough is just around the corner.
This would be the gift that keeps on giving. Yeah Baby.
Enemy cryptography is now a joke. Tanking the enemies economy might be a fun side task.
Even mundane things like modern farming (some of the crew grew up on farms), weather forecasting (important in lots of battle situations too), plastic bags with Ziploc seals, Velcro and who knows how many other things all make an economic impact.
I neglected an obvious counter to this argument, but since no one has raised it...
Giving a Nimitz to Poland in 1939 does not help Poland because they don't have the time and opportunity to make significant changes in time. Poland was invaded by Germany on Sep. 1 and the Soviet Union on Sep. 17. By 6 weeks into the invasion, Poland was military defeated. In fact, it was clear in less than 2 weeks that Poland was losing badly.
If you don't have enough time for the advantages to make a difference, a shiny carrier won't make a difference either.