ac adapter voltage *help*

[lee]

if i use an adapter with 18w, to a mic pre that is suppose to have 23w will i burn it out? the adapter or the pre? the input volts, Hz, and ma are the same. the watts and the output voltage (the pre is suppose to take 160, the adapter is 120) are different.
i really dont want to kill my pre, but i really dont want to pay 30 bucks for a new presonus plug.
please help.