Extension lead between DC Power Supply and TG582n Router

[#1]

What spec do I need, please?
The most common types appear to be either 2.1mm or 2.5mm.  I bought the latter and it is too small.
Technicolor Thomson & Plusnet do not know (They only manufacture/procure/sell them!)
Can anyone give the name of a retailer who can supply the correct cable, please?
Thanks
Mike41

[#2]

The info should be written on the DC power converter plug, sometimes in dark writing. I don't know of that router so can't help any further than that.

[#3]

Thanks for the quick reply!
However, there is no info on the plug or on the power supply itself.
Can anyone else help, please?

[#4]

If you take the power supply adapter into somewhere like Maplin Electronics they will almost certainly be able to 'match' it for you (they're not always the best value but usually extremely helpful for things like this).