Thanks Allan. I just bought the same charger yesterday, The sales guy recommended 30A power supply ...
If you don't have high-S batteries to charge at high amperage, you don't need a large power supply for this kind of energy efficient charger. For example, I only have 2S LiPo and even if I charge them at 10A, 8.4x10x2 is still < 12x15. So my 12V 15A power supply is good enough for my application although the charger can take a lot more.
One thing which might be worth sharing is that the USB port of the charger is very sensitive to the ripple content of the output of the power supply. Originally I was using a Muchmore power supply and my computer could never connect to the charger. After I changed to another power supply with a much lower ripple content, my computer can connect to the charger every time. So if you have problem with the USB connection, check your power supply .