Is there a optimum lenght for power cables?

Your dealer is full of sh!t, to put it bluntly. Explain then why 1.5 meters is the most common length. He's just trying to make more money.
I don't know that there is an optimum length. I've noticed MUCH more difference between different power cord designs and materials than I have between lengths. FWIW, I don't own any 1 meter lengths, but I do own a few 4 foot power cords. The only thing with shorter power cords is that they need to be more flexible. Short AND stiff is a bad combination for power cords.

Also, after talking with many cable manufacturers, it seems like that 'the shorter is better' formula for speaker cables has expired. Most manufacturers today will not sell speaker cables less than 6 feet in length. They now say that 6 feet is the minimum length for molecular stabilization. Or maybe a 3 foot pair just doesn't cost enough. You be the judge.

John

Wheres the science in all this?Its not there thats the problem.Nothing more than a manufacturing ploy to make us spend more money with absolutly no proff of science to back up the idea that a length of cable, long or short will sound better or worse. If you can save a buck keep it in your pocket, because short is good & cheap.

"They now say that 6 feet is the minimum length for molecular stabilization.". I worry a lot about the unstable molecules on my ic's and pets and never trust any person under 6 feet tall :).

All your power cords need to be of unequal length, so the magnetic radiational patterns don't overlap and contribute to an increased electron pull, which is directly related to molecular stabilization. Of course, this increased electron pull is directly associated w/the increased gravitational pull of the moons cycles, so you can only use longer PC's in those periods near a full moon.

You can trust me, as I'm 6' when I'm wearing boots