As
@tangent suggested, I'd test the power supply with meter; it should be about 54 VDC. If it reads good with no load, try a 500 mA load across it, like a 100 ohm 10 watt resistor QUICKLY, as that size resistor will get hot quick (1/2 amp @ 54volts is a 27 watt load). The supply is rated at over 1 amp so 1/2 amp should be no problem. If it drops below 50 volts I'd say it's bad.
If Linksys won't respond or balks at their 'lifetime' warranty, I go along with
@fenderman 's suggestion about a 1star review on amazon or the retailer's site. Below is a screen shot of that warranty you referred to, found ==>>
here.
