I haven't experienced any unusual 540-specific problems, but power bricks in general are notorious for developing intermittents of various kinds. The most common failure mode is for one (or more) internal wire to fatigue to the point of breakage. For a time, wiggling/bending/supplications-to-the-deity-of-your-choice may work, but eventually it stops altogether. I would measure the voltages while (gently!) flexing the cable first.