Cool. There is a fairly simple option where you can run it from the Vicor SMPS, but startup has to be in two stages. You can't readily do a soft-start mode with a SMPS - that works with more conventional loads that are mostly resistive and capacitive, to ease the current surge. When the load is other SMPSs, you have to get through their negative input resistance region without the driving SMPS tripping or stalling in some foldback mode. A way to get around this is to store enough startup energy in a fairly large capacitor - you'd need to experiment and figure out how big. You could run the original SMPS say, into the large capacitor, with maybe some small resistance to soften the charging surge, and only dropping a little bit in normal operation. There is a possibility of stability problems in certain SMPSs with large C, but most should have no problem at all if designed right (with AC feedback from ahead of the output filter, and DC from the terminals or remotely). It would have to be a two-stage affair. First, bring up the SMPS/capacitor section. Then the power switch would connect the Z3801A to the bus and start up. This could be automated too, with appropriate sequencing and time delays. The main thing is to first store enough energy, then dump it in. The very low effective source resistance (mostly ESR of the capacitor) swamps out the negative resistance of the load until things get up high enough for normal operation. The negative resistance will still be there, but will have less effect at normal voltage, and swamped by the SMPS's low output R, after it's in regulation. If you do a conventional transformer/rectifier/capacitor supply, you're mostly transferring the surge into the low impedance of the power line at power-up - same effect, more or less. The parts have to take a bit of abuse during the surge, but usually it's no problem if built to handle the normal load. Ed