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> What information, from what's stamped on the adapter, is enough to tell me whether two adapters are interchangeable?

In general, how to read all the stuff on the label of an electronics device - what do all of these logos mean and which ones are required?

To put an electrical product on market in the USA:

- FCC approval is required, for wireless products in particular. This is regulated by the Federal Communications Commission, an US government agency. They do in turn approve various test houses to carry out tests so that the FCC logo may be attached to the product. FCC are only concerned with _electromagnetic compatibility_ (EMC) and wireless disturbances between electrical products. Wireless products also need to be registered with FCC. They would typically then add the [FCC logo](https://www.fcc.gov/sites/default/files/fcc-logo-black-2020.png) to the label.

  FCC Part 15 as referred to on this label is a directive concerning RF disturbances and emissions for (non-licenced) wireless devices, so I find it rather odd on a part that supposedly does not contain any wireless electronics(?).

- Some manner of _Nationally Recognized Testing Laboratory_ ("NRTL") needs to approve product- and fire safety. Traditionally and most famously UL - Underwriters Laboratories, but one of their competitors will do fine too. Full list of approved labs here: https://www.osha.gov/nationally-recognized-testing-laboratory-program/current-list-of-nrtls

  In your case the triangle to the upper right - the TÜV logo - should be ok.

- The input voltage rating supported should be printed and it needs to support at least 120VAC 60Hz. In case it supports multiple countries it is typically labelled like this one, 100-240VAC with a frequency between 50-60Hz.

- The manufacturer's name or logo should be somewhere on the product too. (I'm not sure if country of origin is mandatory.)

So this product is at least as far as the logos are concerned legal for USA.

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Other stuff on the label:

- The house means indoors use only.
- The double squares means it is internally double insulated and may therefore be used on a mains outlet which isn't safety grounded.
- The USB output voltage and current are stated, as well as the two horizontal lines meaning DC. Which is rather irrelevant info, a USB-powered device should only use as much current as needed and the charger should only deliver as much as it supports, and **it is up to the manufacturers to ensure this, not the end user**. 

  >  Can I safely swap in any other charger that states the same output, or are there other factors I need to consider?

  So yeah you can swap these out with similar USB devices just fine, assuming that the mandatory markings previously mentioned are present on both devices.

  A port with higher current rating will not break your device, if your device is designed properly. 2A just means 2 Ampere max. The various versions of the USB standard support higher currents.

  So it simply wouldn't start overheating when working as intended. However note that various "wall warts" may be designed with internal heat sinks that can get quite hot by human standards, up to some 70-80°C. Older electronics were designed to take down the voltage from 120VAC to 5VDC by, in simplified terms, "burning away" the extra voltage transferring the energy from electrical power to heat ("linear power supply"). Modern ones work differently by switching the voltage on and off rapidly and using the average voltage obtained as output ("switched power supply") and these will not get nearly as hot even when supporting higher currents required by the latest USB standard.

- Efficiency level V, basically how efficient it is to make use of incoming power. This is related to "Energy Star" marking which is relevant for some states in the US, like California which came up with that marking originally. https://megaelectronics.com/the-difference-between-efficiency-level-vi-and-v/

Canada and Mexico have very similar laws as USA but might require national certification with their respective authorities.

At products made for Europe, you would instead of FCC and NRTL markings have the CE mark, covering both. However, CE doesn't actually require testing by a 3rd neutral party test house, unlike the others. So CE in itself doesn't really say much - it got a rather bad reputation for power supplies in particular, where you would rather look for a NRTL marking to ensure that the device is safe, even though that one isn't required in Europe.

A crossed-over waste bin with a thick line underneath is also required for European WEEE compliance, not only meaning "do not toss this in the regular garbage" but also that the manufacturer is part of the electronics recycling program in the country where the part is put on market. The thick line means compliance to the latest WEEE and no line means some older version of it.

Other countries around their world have a lot of national approvals specific to that country, though many accept FCC and/or CE marking (at least Australia, South America etc).

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Now as for what could be the problem with the charger - if it gets too hot to even touch or smoking/burning, then the most likely culprit is IMO a blown protection diode, which when it blows leaves a short between supply and ground, causing a lot of heat but not necessarily affecting the functionality otherwise. This can happen if you had a lightning strike nearby when it was plugged in, for example. It's pretty classic that problems like this appear just after a powerful thunderstorm in your area.

Otherwise there could of course also be some other short circuit or component issue, especially if it is just some cheap low-quality product. 

If you suspect a defect component or short, then you shouldn't be using it as it might have turned into a fire hazard (the fuses in your house might hopefully blow before it comes to that).

Cheap low-quality products may also use counterfeit product markings, even though doing so is obviously illegal. Beware of buying electronics from sites like Amazon, Aliexpress and Ebay - they take no responsibility in ensuring that the product sold is actually legal in your country.