I've got an old phone charger which cannot hold voltage, it goes from 5V to 4V the fault only seems to happen when charger has been on for a while e.g. when warm. Fault happens when high current or low current is being drawn from charger. I've checked capacitors for capacity and ESR and I think they are still good, I've even replaced a cap to get better ESR. Fault still happens it goes slowly from 5V to 4V then interrupts power and restarts. Because it performs on high current (0.67A) and low current (20 mA) the same way I'm guessing it's not the caps but more likely the switching IC. However...
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