The cable box sends a signal to the HDMI-input, not to the PSU. The PSU is directly connected to the power outlet only.
And even if it's the cable box, the design of the TV should be such that it can't harm the PSU. It could blow the HDMI-port, of course.
We are waiting for the third repair of our power supply on our Samsung 55" LED TV in last three months(purchased in 11/11). The repairman says it's the cablebox and of course they say it is not. Anyone else having this issue? When do you call it a lemon?