Contradicting DarkShadow, most routers I've seen use pulse-width modulation power management chips that can handle a wide range of DC input, just so long as the input is stable. I mix 5 and 12 volt inputs freely with my Linksys and Asus equipment, I've been running the same hardware for years, and I've either never or seldom had hardware issues. None of my routers have failed so far.
My knowledge here is not specifically router related. However messing around too much with voltage input can put unnecessary wear and tear on your power conditioning capacitors, generally speaking.
While you may not notice it, one may inadvertently take a device that would have lasted for 20+ years (maybe longer), and cut the useful life of your device down considerably.
This observation is made after replacing capacitors in many NES-001 units (nintendo entertainment systems) from the ~1980's.
I'm sure many of you don't care to "live with" your device that long, but it does make a difference.
**always best to find a decent quality transformer that matches OEM specs**
PS now a little boost in the amperage might not hurt... especially if you have integrated a Fan mod (I'd recommend matching fan volts to your wall wart & borrow power from that transformer directly... as in before the power conditioning caps)
think of volts like the force of electricity, and amps like the amount of electricity.
hitting it harder with the hammer (force) could break it
hitting it softer, the way it was designed to get pounded, but more often (amount) *might* get the job done better
now don't go "frying" your device because of what I said... read up (after all i'm just some crazy guy form the internet) we are likely talking mA, not A here _________________ reenignE esreveR
Resistance is NOT futile... It's Voltage divided by Current!