Voltage problem?

I have a raspi 3 B+ and a powerplug for the raspi with 5V/3A.
But sometimes the octopi web app show me the blitz and the warning, that I have to look after the powerunit.
So, what can I do? The powerunit should have enough power for the raspi.

It's a 5V/3A Micro USB Netzteil ON/OFF Schalter Ladegerät Adapter für Raspberry Pi DE

2 posts were merged into an existing topic: I had a strange lightning bolt/temperature symbol with an exclamation mark popup in my navbar, what does that mean?