try replacing the cartridge filler with tea bags. it seems to work better than the regular polyester filling it came in. it solved the harshness/funny taste, gives a smoother vape, and wicks out the juice better if stuffed properly.
try tapping the threaded end on a desk or some sort. its usually the valve switch thats stuck from the dried up liquid that leaked through the atomizer. its not really broken.
im not too sure but i believe a usb power supply should output at least 1000ma to power a passthrough to effectively power the atomizer. mah is the capacity; what you need to know is the ma (output)your power supply delivers. if your passthrough came with a built-in battery (usb charges the battery then battery powers the atomizer), then a power supply with a lower ma might work. i personally use an APC Mobile power pack i bought off ebay for $30 and works great.
there are several people who replaced their fillers with tea bags with much success. it gives a smoother vape on any liquid without the harshness typically experienced when filler strands are stuck into the atomizer. i personally use the bags by lipton tea in my janty and dse901. (credit to sub???pete at ecf)