The WNR3500L takes a pretty standard 12vdc 1a power plug. Available for under $10 with free shipping even to Hawaii at a few sites I checked.
You could also reset your router, if you ever wanted to. You won't lose the version of firmware on it. Linksys doesn't do that, you'd have to open the router and jumper a couple of chip pins to wipe the firmware.
If you want the beta firmware for your old router, look here: »/r0/down···code.zip
It's BEFSR41V3_v1.06.05_000_code.bin if anything that should give you a file name to search for on your XP machine.
It was posted on this thread, 7 years ago:
»Re: [ENG] TM402P reset--
Two is one, one is none. If it's important, back it up... Somethimes 99.999% availability isn't even good enough.