There are two kinds of wall warts. The traditional transformer based ones, which are large, heavy, and poorly regulated, and the new all-electronic ones. Because they were cheaper and more reliable, the older ones were more popular, but s the price of copper (for the transformer) shot up, they lost the price advantage and now almost all the new ones are electronic, with a digital (not linear analog) regulator. The new ones regulate very precisely, even cheap no-name ones.
If you have an old one that is poorly regulated, you can often splice in s 3-pin linear regulator (78xx or 79xx chips will carry 1-1.5 amps as is) in the output to clamp it more tightly.
Fun facts about wall warts: It can cost $50,000 to get UL certification for a device, so manufacturers like to certify one wall wart, and use it as the external power supply for many devices. And, wall warts were one of the leading causes of home fires in the US. Mainly overheating transformers.