The power cable can’t generate power however as mentioned the wrong sized cable, I.e. too small can restrict power. Put the OEM cable back on and if the problem persists, contact McIntosh or at least Audio Classics. The problem is in the unit and they will suggest a possible fix or ask you to send it in for a check up. I have dealt with McIntosh many times over the years and they are great people to work with. They have an enormous pride in their products and equal appreciation for their customers.
10 gauge power cord. Too much power for tube amp?
Tube amplifiers tend to be sensitive on incoming voltages. Is there a chance a bigger gauge power cord like 10 gauge may not be a good thing?
My amplifier tends to shut down occasionally upon start up. maybe moving to a higher gauge might be better. Does it matter?