There are generally four things that seem to cause this low power message/warning.
1. Using an underpowered USB port for power. [Try using a different USB source. If using TV USB port, use wall power instead.]
2. A failed/failing USB power adapter or cable. [Try replacing with a USB cell phone charging adapter and cable with micro USB on device end].
3. A failed/failing power source. [Eliminate any power strips, surge protectors, or USB hubs for troubleshooting and plug directly into wall outlet. Verify 120volt at wall outlet.]
4. A failed/failing Roku device or possible firmware/software issue. [Try performing a Factory Reset on the Roku device. If no go, then replace Roku device].
I can't argue that Roku support and contact options need improvement. They used to have a pretty robust phone and email support that was quite responsive.
If you try all the above steps and your device is less than a year old, then you should submit a warranty claim (https://support.roku.com/article/208757058).
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941