The Spectrum requires a good branded power supply of 5v/1A. If you are connecting USB sticks and multiple game controllers to the The Spectrum you may need a larger power supply of perhaps 2A, such as one for a tablet.
If you are experiencing any instability, such as The Spectrum shutting off or display issues, the first things to check are the power supply and cables. It is a good idea to change power cables as well as power supplies if you suspect issue, since they can also introduce power issues.