samcheetah said:
my mobile phone charger is simillar to the one mentioned by Someone Electro. it says that it outputs 5.7V @ 800mA and its really really light and as thin as my mobile phone itself. so does that use a switching regulator with a switchmode transformer. i highly doubt there will be anything like a transformer in there because as i said its very light. i know i should open it but it has odd shaped screws.
They will be security screws, there are various types, and you can buy sets of tools to undo them.
Switchmode transformers are very light, they use ferrite cores rather than iron, and the high frequencies employed make them small. Your charger output is only 4.5W, so it's a very low power supply, a switchmode transformer for that could be tiny.
It's also possible it uses a simple capacitive dropper off the mains, but this doesn't provide proper isolation, and the dropper is likely to be fairly large.