When two bricks that are not exactly the same (wire size, turns ratio, etc) and run in parallel they run current through each other to get the output voltages to exactly match. You loose some capacity of the bricks to heat buildup in one or both. If your layout needs more than 180 watts then block it and use one brick per set of blocks, never allowing bricks to be interconnected. How big the effect is is a function of the differences in the bricks designs.
A couple years back I too pursued the 180 watt brick only to find them gone (did they ever come back or is this the same shortage as about two years ago?). My layout is small and I could run all my accessories and the track on a single 180 watt brick. But that is academic when you can't buy one. So I put only the track on one 100 watt brick and all the accessories on another 100 watt brick. The 100 watt bricks were MTH units with extremely slow circuit breakers. I indeed did get to see welding with derailments. So I added a magnetically triggered aircraft style circuit breaker in series with the track. It trips in less than a second and saves having to tear open my MTH TIU to replace the fuses after every arc producing derailment.
LDBennett
