My guess (and it is just that - a semi-educated GUESS) is that it's a
switched mode power suppy (SMPS) which are almost all regulated. I've a
15VDC/1.0A regulated SMPS which weighs about 4 oz. while all of my 12V
magnetic transformer style power supplies weigh 12 oz or more. But the
heavier transformer type could still be regulated.
The only way to be certain is to contact Linksys Support and ask them,
telling them you lost the original power supply.
Otherwise, if you have a friend with a voltmeter, you can measure it. Or,
assuming you are going to buy the replacement at RS, ask your friendly RS
rep to measure the one from Linksys. If regulated it will measure 12V while,
if unregulated, it will measure more, up to 17-18V.
One final clue is that California, Europe, East Asia and other regions now
have efficiency standards for wall transformers that can only met by SMPS
types so my guess is that Linksys will be using them - I know that D-Link
(which I use) does so.