The DC5 is the only one that will fit under a Pedaltrain Nano, I recommend it (Hotrox sell them).
I tested plenty of pedals on top of the power supply, into a headphone amp with the treble whacked up to check for noise introduced by pedals being too near the power supply. There was a barely detectable hum introduced with some pedals when placed directly over the supply. Certainly not an issue, even when recording. The Diamond compressor picked up loads of noise when it was anywhere on the board though, even in bypass, yet was fine when placed directly on the floor!