There’s a FAQ about the PWR_FLAG here: ErrType(3): Pin connected to some others pins but no pin to drive it
It’s worth reading to understand the reason behind the ERC message and how to deal with similar situations.
There are a few solutions you can use:
- Ignore the warning
- Put PWR_FLAGs on the power lines
- Make a modified copy of the power jack where the power lines are of electrical type Power Output
Addendum: That FAQ is a bit dated and the exact messages have changed. Somebody more keen than I am should write an updated FAQ.