I'm trying to use my 250GB external USB SSD on my S5. But unfortunately my powered hub broke... So my only choice is direct connection. The SSD uses 0.9A @ 5V, and I have no clue about how much power my phone can pump out - Please help
OTG devices can provide up to 500mA, but in realistic terms, handheld portable electronics don't have 500mA to spare for external loads. 100mA is a commonly accepted realistic maximum.
So basically, don't expect any device that draws over 500ma to work at all without an external power source of some kind, but depending on your device that maximum may be closer to 100ma in reality.