Do good power cords have to be stiff?

Audio Envy. Both the P series and the M series are very flexible and sound quite good.

Triode Wire Labs.  Pete's cables are flexible, but more importantly sound great.  Open, transparent with tremendous PRAT.

The Puritan sorta reminds me of a wet noodle.

I don't think you could find a PC more supple.

I get that 12-14 awg should be enough wire for most components, but when I plugged in my 650 wpc monos using the 7 awg WE PCs it was one of the few times  I perceived that cables went beyond simply making a difference to making a definite improvement.  The 7ga cables are 6 runs of 10ga wire into each Furutech FI-11 connector, 2 runs each for pos, neg, and ground.  The 10ga version are more flexible and certainly big enough to handle any audio related load, but for some reason it seems the bigger 7ga cables sound even better on my big amps.

a great power cable that is very flexible: e.g., VH AUDIO Airsine.