The stock wall wart PSU is generally fine if you do not want to use USB powered peripherals, like a WD Passport drive. Even then, it can work fine for a while but on a peak load transfer things start to get dicey and you can end up with disk errors.
I looked at the various current draw reports. I did my own calculations. I gave the stock PSU the benefit of the doubt. It should have been fine. Yet, in the end, after numerous occasions of failed transfers and disk errors I gave up. I purchased a 5A inline brick PSU to feed it and have not had a problem since.
It is telling that for box like the Popcorn Hour A-400, a 3A inline brick PSU is supplied as standard and I have never had a problem with one of those, regardless of what I connected to it...