I've been using a 9v SMPS for a while for all my pedals but recently got hold of an EHX Holy Stain which HATES it. I've done a bit of a search on this and it seems to be quite a common thing with not only the Stain but the Grail as well. If you're not using the EHX PS you get a pretty loud digital mosquito whine. I lent it to a guitarist to try out, warning him about the excess noise. He plugs it in, daisy chains it up to his Boss TU2 tuner DC out and....... SILENCE! I get really excited about this- I've made a few pedals and one of the tricks used to overcome a poorly filtered PS is to bridge across the terminals with a fat-assed capacitor. This shorts out any AC signal and leaves you with clean(er) DC voltage. I'm thinking the TU2 has a filter cap which is doing the filtering for the Stain. So I go home, plug the Stain into my TU2 and..... "eeeeeeeeeeeeeeeeeeeeeee". mad Plan B- I reach into the bag of tricks, pull out a 9V plug, 1000uf electrolytic cap and attach it to the daisy chain. It's better (about 50%) reduction, but still there. Plan C- added the uPOG into the chain- success, silence. I'm thinking it would be really handy to develop my little 'Plan B' DC filter to be added to a daisy chain (if there isn't such a thing already) to filter bad PS's. $1 worth of components could make more expensive filtered supplies unnecessary. Can anyone shed a bit more light on the circuit bits of the TU2 and POG that would be 'cleaning' the DC?