I finally got around to building my MERG booster. The booster is a kit available from MERG. merg.org.uk You need to be a member to buy their kits but it is well worth the price for the information available to you and the other kits they have in their kit locker.
The assembly went very smoothly and I followed the instructions very carefully. There is nothing tricky about the assembly but you need to have some soldering skill. I suggest you buy a piece of vero board or bread board and some cheap components and practice if you’ve never soldered before.
The power supply I used is a switching power supply I bought from China on eBay. Something like this:
This one is 18V but there is a pot to adjust it down to about 14.5V, perfect for DCC.
The booster works exactly as advertised with both my NCE Power Cab and my DCC++ Base Station and I highly recommend it.