>>"Simple question. Is it ok to use a 10a 250v power cord in the united states on 110-120v products?:<<
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Look on the outer jacket of the cable. Does it give the wire size? For USA power cords it does. Example, 18/3, 16/3, 14/3, 12/3, ect. Good chance the cable is equivalent to 16/3. Might be ok, maybe, for a CDP but I would not recommend it for a preamp and definitely not a power amp. Jmho.
Jim