Hi there,
From my experience, all extensions are the ones without capacitors. A capacitor is mainly for the main socket, ie NTE5. If you do have an NTE5, its easy to add an extension. Just take the front plate off, and it reveals what we call a test socket. If you look at the back of the plate you just took off, you will notice 6 punch in slots, where you punch in the extension pair.
A 3A should suffice.
You may have to take off the test socket plate to run your cable through the mounting box, and through the hole to put on the front plate.
Use punch slots 2 and 5. (2 is the A wire, 5 is the B wire) and do the same on the other end of the extention cable you are installing, (2 and 5)
would recommend you use the White wire, Blue stripes as A (2) and Blue wire, White stripes as B (5) with your extention cable. They are twisted pairs, so you cant really lose them or go wrong.
Whatever you do, dont wire it directly to your dropwire coming into your property, or UG cable if you have an NTE5 setup, as you're not really allowed to touch the external network. However, its normally permitted to use the front plate to add extensions.
BTW, personally, wouldn't bother with a ring wire. (punch in 3) Sometimes causes more trouble than its worth with certain ADSL setups.
Any further questions, dont hesitate to ask. Sure one of the engineers on here will be able to guide you
Good luck!