I've upgraded a Richwood Explorer with a Warpig/MQ set and a Raven West PRS Hollowbody clone with AII Mules. In both cases I updated all the hardware and all the wiring. Neither of them feeds back more than any other guitar I have. I would think the cheap pickups and hardware would be more likely to cause feedback over the caps. Perhaps your tech meant that upgrading to good capacitors with cheap pickups would lead to more feedback? Even that is dubious, but more plausable.