DSIXL charging light flashing irregularly

When I connect my NDSiLL to the charger it showed no signs of being charged at all. The motherboard looked almost new, it has no signs of corrosion, no missing components and no damage at all. I tried a new cable, cleaning the port, bridging both fuses, replacing the battery, but nothing worked. Out of desperation I updated the system and miraculously the light began flashing. However, it's irregular, unlike the blinking light that other people encounter. The charging icon is also shown briefly when the charging light comes on but vanishes just as fast. I checked and there's a constant current passing through the charging port to the motherboard, which eliminated the charging cable and charging port, but I have no idea what went wrong.

I also plugged the cable into a mac and somehow the light was constantly on for a short time, but disappeared after a while as thought the mac refused to charge it.
Now, the issue could be that I wasn't using the stock power block but a charging cable, which could have different charging voltages or whatever, but the cable worked on my 3DS and on a broken motherboard. I suspect that it's an issue with the charging cable but I need to know for sure. Did anyone else came across this ridiculous issue?