The very problem my 7-year-old "engineer" and I were troubleshooting today.  While our design wasn't quite as perilous as the "before" here, I think we are (were?) running into is the cable length.  The supply is a USB rechargeable brick (ModularVille is perched atop the pool table, so no wires are key.)  

The build-out involved a supply line that branches out to each of five city blocks, and each block has 2-3 pico street lights/interior lights, and 3-4 strips.  At first, it was stellar, then grew dimmer over time (despite re-charging or even going onto wall power).

Our short-term solution today was to run a "booster" wire (2x 24-inch) out to the two most remote legs and, effectively, connect the "tail" ends directly to where the USB comes into an expansion adapter. Some wise man once preached to me about how DC runs need to be short, AC is more forgiving... and absent reducing wire length, the direct-run gave us a boost... and enough to offset the flashing dim-bright-dim-bright of the flashing pico traffic light.  

I'll have to sketch it out for grins and giggles, but plug-and-play it is, but when you're covering 24 square feet (and growing monthly), the "dim" happens.  ;)

Rob Klingberg I've no doubt it would be helpful, but if i were to put on my business owner hat and the wise wisdom on Shark Tank, I'd perhaps stop short of calling it a formal direction.  (The comment was relative to how an entrepreneurial spirit can run afoul of meeting a market need versus doing so absent a vast market demand.)  While it would be helpful to me, I'd speculate -- wholly without any evidence -- that many (most?) installs are smaller scale, and this would be very niche.

That said, the current product line is more than suitable to offer the needed pieces to remedy the effort... placing my order for expansion adapters (two regular, two micro)... which actually solves two issues in one swoop:

• Eradiacare the need for the as-is: I currently am setup with an expansion adapter to give me a "leg" into a 2:1 pico, which snake into pico streetlights
• Eliminate the need for ANOTHER expansion adapter to infuse the booster legs, since they'll all be placed at the end of the lines.

So while a noble offer, I'd defer to your better judgement.  And once I finish the entire 4'x8' base, and solution my other issue (I'll start a different thread), I may regret my deferral of such a widget.  😉  If anything, I'd ponder if a larger gauge wire with the regular plugs may be of greater merit - and easier to market and construct - as I'd imagine the larger gauge would have less resistance for the longer lengths... thinking you can get a gigantic power supply, but if we're still trying to shove all that juice into a... 26ga? wire... there's only so much capacity that could effective transit down the pike.

___

Visually, we've got this puppy built out with a 5VDC USB power supply (upper right), and the red dotted lines were the original wiring branches.  The purple are the "booster" lines that run, without in-line load, out to the various blocks to boost the supply.  (All are/will split from a regular expansion adapter with 24-inch wires in line.)

(The starbursts are pico street or accent lighting, the 2-LED strips are inside the ground floors only -- to minimize conflict during play time -- until I further delve into the experimental power-capped studs...)  Red lights are flashing red pico streetlights; one current (lower center), one future (upper center).

Another solution is to make a thicker extension cable.  I used some of the Connecting Cables and 26 AWG stranded wire and that helps the dimming solution.  A recent variation is I used 22 AWG solid wire inside my brick built roads as the power distribution system (more details in a future post).

Rob Klingberg These great guys back east are making these teeny wires... ;)

The city itself is perched on a plywood sheet on the pool table, with a flannel sheet covering the wood (really to protect the pool table, but I digress).  The wires are small enough that they just lay under the plates, and every 24" they pop up to go into the expansion adapter, which just tuck into the nearby building / accessory / recycle bin interior, etc that's nearby.

I like Jim Pirzyk 's notion of larger gauge wires, I've just not bothered to dust off my soldering iron from that LED project for a (real, non-LEGO) fire engine when I re-did the gauge cluster in LED from incandescent.  

But... golly... if there is a formal direction for a bigger power supply, I'm in for one.  Or two -- the kid has been making noise that her Friends-Disney-Jungle-Pet-Rescue-Town lacks adequate illumination.  But I'll distract her with getting The Castle lit first.