10 gauge power cord. Too much power for tube amp?

No chance 10 gauge has any negative effects… the gauge unless tiny is not going to change voltage fluctuations. In every case… for instance in installing direct lines, and power cords, larger gauge has produced better sound quality.

Also, @mulveling +1

Amplifier shutting down is going to be caused or enabled by some issue not related to the gauge of power transmission.

Something’s going on, but it’s not the power cable.

I’ve used one of these on a tube amp. It lived up to the hype, but after many scotch tape repairs to the candy wrapper (as approved by Pierre’s staff) I switched to over priced fancy stuff.

Just in case you didn’t, did you check the power cord for nicks? If the male and female ends are operable did yah look there too? This is 99.8% sure not to be it.

Did you switch cords? Tap tubes for microphonics? Swear a lot?

The amplifier is a Mc2301 from McIntosh that's giving blinking red lights after warm-up frequently. Power tubes have been replaced with new ones, maybe it's a signal tube. Sometimes it works fine, as long as amp stays on for at least a minute after warm-up.  

Power cord has nothing to do with the amp shutting down. The protection circuitry is kicking in. Don’t know how it’s wired but it usually senses overcurrent at the output stage. This can be caused by a failing power tube, a total loss of bias voltage or loss of bias at an output tube, an intermittent short in the output stage or a mismatch between connected load and speaker tap.