The nameplate amperage is the maximum the device will draw from the power outlet - immaterial of what the output is. Thus if your output socket can supply the nameplate current, you are ok. Your output current will (In the case of a power supply) be (Iin x Vin / Vout) x Efficiency (anywhere between 99% and as low as 45%). As long as you do not grossly overload the device, the nameplate current will be the max that you draw from the supply.
Does this help?