For an exaample of load and line regulation my Kikusui Pad 70-5L an old linear model is 1mv, yours is supposed to be 3mv, as i said added digital circuits / converters add some loss.
Just saw you have 16 bits resolutions DAC's, and a Pic 18f85j10 and 16 bits ADC, pretty good stuff in there, i'm impressed
In smps when the fuse generally blows up, many transistors in the switching section has gone bad, its a last protection measure. Still havent found my HY3010E-2 troubles, the main smps section has severly busted ? lots of precision resistors and mosfets later, still a paper weight.
But yours is based on a toroid transformer a good design choice, love to see x-former secondary relays switching, to minimize the heat dissipation.
I think you have the service manual, just foun out this ? :
http://www.eltest.hu/pdf/GPD3303SM.pdfOn page 89 we see the input circuit, i dont see any EMI/RFI filter ?! Not sure you could cram one in there easily ?
Would be nice to measure the inrush current when you start your supply, you could change the fuse for an slowblow model ?