Power Adapters may become warm (or very warm) when charging devices - but should never become to hot to touch.
Beware that some third-party Power Adapters, in particular “economy” items from less reputable sources, may not be manufactured to Apple OEM standards - and perhaps lack many of the built-in protections that you might expect from better equipment.
A general observation for contemplation…
Use of a cheap Power Adapter is false economy when you consider the relative cost of the device that you may be charging. The Power Adapter has the capacity to cause irreparable damage to anything to which it is connected; poor power regulation, or an electronic/electrical fault, can destroy connected devices. Device warranties will usually not cover consequential damage.