A company's net worth isn't very telling for this.
I couldn't find 2019 numbers, but it looks like they sold 217.72 million iPhones in 2018. If we estimate cost of production of adding the charger and cable at $15 each (including R&D, added packaging, added skipping costs, etc.), that's a direct hit of just over $3 billion to their revenue if they don't adjust their pricing. Another source I found showed iPhone sales accounted for 52% of Apple's revenue. That's nothing to bat an eye at.
What I would love to know, but couldn't find out, is the net profit margin on iPhones. I found many gross profit margin numbers, but that only factors in the direct costs of manufacturing, not including other related expenses. I.e. Advertising, researching, office staff, etc are not included. That would be the real number to pay attention to. Even with them being one of the top manufacturers, they are still held to the laws of market competition.
Now factor in their declining market share, and stuff like this makes a lot of sense.