Could be the power bar, could be the cable.
I would wait to hear back from the seller.
Here in *theory* taking it apart and checking the cables should not invalidate the warranty since you do have to pull miners apart now and then to clean out the dust.
In reality, since you bought it from a reseller through Amazon, they can make any rules they want about what you can and cannot do. I would wait to see what they say.

If they don't respond or fix it for you get Amazon involved as early in the process as possible.

-Dave