USB charger suddenly fails to work

Hi!

for the second board (blue one) I'd start by checking that resistor down near the main input wires. Looks like it's a fusible resistor so it should show close to 0ohms if it's good, next up I'd go ahead and check the mosfet, it's underneath where you see the large solder pads, it has 3 distinct tracks the large ones are drain and source and the small one is gate, If you have a multimeter you can use continuity mode, there should be no shorts between any of the pins, if that checks out fine go ahead and check the bridge rectifier, it's the 4 pin IC on the edge of the board, should not be shorted in any way, go ahead and check any secondary side diodes also. If those all check out then that leaves the feedback circuitry or driver IC which unfortunately is where I usually draw the line, as they're a major pain to get hold of and most usually don't even have an identifiable part number.

For the first board it's the same procedure, however I don't see any type of fuse as you mentioned, not even a fusible resistor, IMO that's a bit of a fire hazard as mains goes straight into the bridge rectifier. The mosfet is also likely integrated into the driver IC hence it only uses that one 8 pin IC. Given that the board is not totally toasted I would think that the fault is on the secondary side not primary (still go ahead and check for shorts around the IC and bridge rectifier etc.. just to be sure), so I would check that big diode right next to the yellow transformer and usb port and see if it's shorted.

Check the capacitors on both boards if you have not done so yet, as they're one of the most likely points of failure.

Great to see a fellow Maltese person on this forum!

Best of luck!