I’ve eaten at a KFC in Kentucky and a Boston Market in Boston.
They tasted the same to me. 
I’ve never had really fresh raw fish (everything you get in almost everyplace, even in Japan, has been frozen) except in one place in an historical town on the Japan Sea side called Kanazawa. They had their own fishing boat, and caught the fish locally enough that they didn’t have to ice it down so much it was frozen. They caught it in the morning, served it in the evening, and it was ambrosia. I ate it as sashimi, and I will never forget it. Someday I hope to go back there and find that place again.
You have got to try McDonalds food at its birthplace in Des Plaines, Illinois. It is so much absolutely the same as everywhere else.
Chicago-style pizza doesn’t seem to translate well to other areas. Likewise, sourdough bread’s just not the same outside of San Francisco, probably because the “mother” (150-year old or so yeast) doesn’t travel well.
Chips (with or without fish) in England are spectacularly better than any chips I’ve had here. At Dionysus at Tottenham Court Road you could get a cone of chips for a quid that are the most delicious thing imaginable.
You can’t get anything close to them in Toronto (at least, I haven’t found it - if you can help, please let me know!), including at the vastly overpriced imitation-English chip shop, and at the chip truck (definitely chips, but not very good). It is possible to get somewhat decent fries (including one pub that does a very passable imitation), but it’s not the same.
I did have delicious french fries (frites) in France, too.
Curiously enough, there used to be a restaurant in Boston called (I think) Warburton’s that served “Authentic English-style Cheddar Cheese Pizza”. I’d never heard of such a thing before (or since), but it makes some kind of sense that if there was an “authentic” English pizza, they’d try to make it with Cheddar Cheese.
Never heard of it being passed off as American, though.
On the flip side, I once ate at Unclde Buck’s American Cuisine in Scotland, just to see what it was. There was a rather tough steak, and the ice cream sundae for dessert had oddly light-colored chocolate syrup.
Australia probably contains some of the most authentic and highest quality Chinese food outside of China (including the Flower Drum in Melbourne which is rated as the best Chinese restaurant in the Southern Hemisphere) but whenever we go back to China, the food there is always a revelation. Flavours just seem more crisp and defined, things taste more of themselves. Tiny shrimp in Shenzhen, plucked out of the ocean an hour before cooking, steamed whole fish in Guangdong seasoned lightly with soy, Spicy rabbit studded with a profusion of hot chillis in Sichuan, Clay baked chicken in Shanghai, pulled noodles in Xian, spicy lamb skewers in Beijing and ephemeral dumplings, soft as clouds in Machuria. The food there simply tastes like nothing you can get anywhere else. It helps that we had friends everywhere willing to show us a good time. Despite people waxing lyrically about street food and roadside shacks, some of the best meals we had in China were in restaurants that looked like palaces, ensconced in private rooms. The average Chinese is not ever going to see this food, even if they could afford it because it requires contacts and influence to get a table. Still, it was some of the most amazing food I’ve ever had.
On the other hand, Hamburgers I had in Hamburg tasted pretty ordinary :D.