In case you've ever wondered about what's equivalent between US and UK chocolate, here's a guide. I have eaten chocolate extensively in both countries and so can hopefully enlighten anyone who is curious. I'm sure more will come to me later at which point I shall update.
Cadbury's <–> Hersheys
There's several Cadbury's brands available in the US, such as Dairy Milk, Caramel and Fruit & Nut. However, if you look at the wrapper, you'll discover that they are manufactured under license by Hershey's and they've made sure to give it their distinct “tastes completely inedible” flavour to it. It's worth trying once because they have also faithfully reproduced the Cadbury's flavour in there, so it really is quite disgusting.
You can find imported Cadbury's bars in some stores and on Amazon in the US but some of them (like the above Dairy Milk/etc.) can be harder to find as Hersheys sues importers trying to get around their inedible filth.
Hersheys itself
No UK counterpart, it's such bad chocolate that I don't really consider it an edible food, it's more of a decorative wax. I find it offensively bad.
Mars <–> Milky Way
For whatever reason, the sort of thing you'd consider a Mars bar in the UK (nougat with caramel on top) is a Milky Way in the US. They're very approximately the same, but the US Milky Way is a bit bigger, and softer nougat. My dad notes “they're how Mars bars used to be”.
Occasionally you can buy Mars bars in the US, I don't know why.
Milky Way <–> Three Muskateers
The Milky Way in the UK is just a small bar of fluff. In the US the Three Muskateers is a huge bar of fluff, and the fluff is heavier. It seems they never put it through the “this is actually a health food” marketing attempt Mars did in the UK so it remains a giant bar of nougat. Similar to the Milky Way Mars Bars, my dad also notes “this is how Milky Ways used to be”.
Three Muskateers Truffle Crisp
For a time in the US Mars sold this strange bar, which was kind of like a Twix in that it was two fingers each of which contained a crunchy thing with a soft thing on top, all wrapped in chocolate, but instead of biscuit the crunchy part was a toffee similar to the type used in Cadbury's Crunchies, and the soft part was nougat instead of caramel. These were also marketed as a “health food” by implying they were low calorie as is Mars' tradition but they were cancelled shortly after being introduced, which is a shame as they were very tasty.
Maltesers <–> ???
For some reason Maltesers aren't generally available in the US. Sometimes you'll find them (in huge buckets) in Costco and if you get vouchers from Mars corporate they'll have the Maltesers logo on them amongst the other well known brands, so I'm really not sure what's going on.
There's a few things that look like Maltesers like Milk Duds but they all taste terrible.
Galaxy <–> Dove
This one's easy – Dove chocolate is just Galaxy chocolate, though the latter is slightly more greasy for some reason. They even use the same font in their packaging, though “promises” are more of a thing in the US. Available with caramel inside/etc. just the same, though I think the caramel may also be better in the US, Galaxy Caramel caramel is a bit thin.
Minstrels
Not available in the US, they're like giant M&Ms. M&Ms themselves are obviously available in both countries though in the US they're made with high fructose corn syrup and last I checked the UK versions were not, so I assume that just makes the US version worse in some occult way.
## Easter chocolate
Why won't it correctly format the above header? Ah well.
Easter eggs
Americans don't really “get” easter eggs, which is a huge oversight. Instead they do stuff like buy little reusable cardboard eggs and fill them with random (often bad) chocolate promises and such. Easter eggs are objectively better.
I did see an easter egg in one of those big “excess inventory” shops like Marshalls, but it was clearly a “novelty”. They also had a giant chocolate American football around superbowl season. I assume the chocolate quality of these was extremely low.
Hershey's also sometimes sells a chocolate easter egg, using Cadbury's branding, but as usual it's inedible.
Cadbury's Creme Eggs/Mini Eggs
Hershey's also make these under license. They taste terrible and are nothing like the UK versions beyond the vague concept of “some kind of shell with some kind of filling”. They're somewhat easy to recognise as even the packaging is kind of sad and weird compared to Cadbury's UK graphic design.