I was wondering what would happen if you gave a multimeter in the DC a super bumpy DC. The cap will definitely be helpful.
Multimeters use double slope integration AD conversion with relatively long times so are insensitive to the AC component on DC ranges. Some modern ones are using a sigma-delta AD with a digital decimation afterwards, which is generally a modern equivalent of good old integrating ADC.
But you never know how many corners are cut in a cheap design)
Again, do not leave the ampermeter load in this circuit disconnected even momentarily as this will fry the diodes and blow the capacitor. You may add a safety bypass of some kind (like ~5 pieces of 1N4007 diodes in series) if you can't be sure.