I looked up the specs on that and it's a 7.5 V 1A power supply. The one that I received is a PowerBook adapter, but it's number M5140 and is 7.5V/2A. Close, but no cigar. I take it I shouldn't use that since I might blow it up. Right?

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It's probably just fine to use. The basic rule is that it's the voltage that it's too high voltage that matters, not amperage (just as long as you meet the minimum amperage at the correct voltage). There are always exceptions to rules, however. We had a similar discussion in a thread about PowerBook adapters on Macintosh Portables.