I had an old Pittsburgh Modular AC Cell 90 power supply.  It is as simple as you can imagine.  Uses a 2 amp AC wall wart with bridge rectifiers and 7812/7912 three terminal regulators.

Cell 90 AC Supply

I am using this as a temporary supply for my Mescaline case.  I put it into a 16 hp blank panel and added a banana jack for grounding.

Mescaline Case

I went searching Mouser.com for a 12 volt RECOM power regulator.  I have used their 1 amp regulators, R-78C12-1.0, which are drop in replacements for the 7812.  I found the 2 amp version, R-78B12-2.0.  That’s what you see on the left in the picture of the power board.

When I powered it up with all modules connected, it failed!  Less than 4 volts measured on the 12 volt output.  Why?  It couldn’t be load, because the load here is less than 500 ma.  By selectively unplugging modules I found that it worked if only the Mescaline Mental or the Motion was connected, but not both.  Looking over those board, I noticed very large capacitors near the power inputs.  Here is the back of Motion:

Large capacitors near power connector

They indicate 470uf, 25 volts.  I measured them.  They are in parallel, making around 1000uf.  Two modules like this add up to 2000uf. (Mescaline Channel doesn’t have these large caps.)  That can make for a large surge during startup.  To test my theory, I unsoldered one capacitor from each board.  Voilà!  All is good.  Apparently Folktek engineers figured they would try to accommodate poor 12 volt wall warts by adding a large capacitance on the incoming line.  I don’t need that, because I have a super-duper RECOM regulator.  But it was a bit surprising to see it balking at a large capacitance load.