yeah chack the main solder joints.
Also it has been confirmed that there is another source of the sparking, and yes, it is actually in the connection between power cord and PSU.
From what I've found, this issue is far less common than the solder joints actually breaking, but, sometimes, the pins pn the PSU plug don't make a very good connection with the power cord, and can spark, or at least go high resistance and get very hot.
I have heard many cases of the replacement (huge) power cord tripping very often, even when there's nothing wrong with the psu.
My guess is the cord has a very sensitive current limiter, and if the current draw is even slightly higher than it should be, it trips. So yes, lots of LED's or other goodies running off your psu will cause it to draw more current, which will not only up your electric bill

, but possibly trip the replacement cord. Even on an unmodded box, it seems that the current limit is too sensitive and will trip randomly.
IMO the wall wort power cord is causing more problems than it is fixing.
If your solder joints are ok, and the old cord doesn't feel excessively loose, just run your old cord if the new one is tripping all the time.
As for the "normal" looking cord received for 1.2-1.6 boxes, use it. It does have that extra little lip on it, which will save some strain on the power connector.