Jim said: The question is really more one of "how much filtering do I need to design into the downstream power supply circuits"
The answer of course depends on the source and receiver of the noise. Common USB type systems and accessories are built to maximize cheapness, pass EMC testing well enough to get by, be small, and provide the required power.
The normal-mode ripple and noise can be made as good as necessary with enough filtering and active regulation, at one point of use. The bigger problem is the common-mode signals that permeate everything.
If you're using a compact, battery-powered SMPS to run your OCXO, then you can take advantage of the situation by "canning it up," as I always say. Don't have a bunch of cords and cables and wallwarts going all over the place - everything will carry some common-mode current and make a mess. If you package up the battery/power supply unit along with the OCXO inside of a metal case that more or less completely encloses it, then it will be very much easier to get control of the C-M currents within the box, and make them nearly invisible outside the box.
Picture a metal box with the proper guts inside, and say, the outside sports a BNC 10 MHz out, a power switch, maybe some indicator lights, and a charging port. All the action inside can be well hidden from the outside, and the desired output signal will have one ground reference point. During charging, there will be another C-M current issue due to connection to the port, so the EMC performance will be degraded somewhat. But, that can be improved internally too, because the system is mostly canned up.
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