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You might be OK, but DAC performance is usually improved with a stable regulated supply (I am assuming that there is probably some additional internal voltage regulation in the V-90 DAC but I'm not sure). So an unregulated DC supply whilst it might be OK may output a slightly different (higher or lower) voltage than the regulated one and this could change with changes in mains voltage or loading from the DAC. You are better off replacing like with like.
PS Are you talking about replaing a plug-in wall wart type power supply or one of the optional Musical Fidelity power supplies?