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.
The Spectrum is not compatible with fast-chargers, so please use a standard charger that can provide a fixed 5v at a minimum of 1A.
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.