I just had an application where ground capacitance and stray capacitance of all power supply options (Switch mode wall warts, grounded switch mode supplies) was to large and spoiled measurements by injecting relatively large mains frequency dependent voltages.

I actually helped myself out by building an optical power insulator (a LED driving a small solar panel).

I wonder why I found no low capacitance (stray and to earth) power supplies.

All supplies I checked out either showed symmetric mains capacitance (providing about half the mains voltage at the output GND) or ground connection (output GND tied to mains GND).

Is there any special type of supply that connect mains or earth in the smallest possible way? How would it be named?