I have no direct experience with ROKU's being nasty, but anytime I have an intermittent issue and the product uses a modular power supply, I check the power supply. Since power supplies seem to be commodity items, it makes sense to send the purchasing agent out to find the deal of the century. Shaving a few cents off the budget gets lots of "attaboy" for the agent, an off the path power supply, and headaches for the support crew.

Some units have such a bad history with me that I assume the power supply is at issue until proven otherwise. This saves an incredible amount of diagnostic time.