I recently purchased a Hitachi Visionbook Traveler 3745 and it is missing an AC Adapter. The rear panel states that it needs 15v 2.3A 30W Adapter. However it has a sticker on the side that says, "Warning Use only AC Adapter provided with system". My question is regarding whether I can use any simliar spec adapter with the right connector tip? What is the leeway i have on voltage and amperage?

The answer is, "nobody knows how much you can deviate from the specified voltage except Hitachi, and they've already given their answer." There ARE always adaptors for sale on ebay, both original and "aftermarket." My advice? Don't screw around. Any laptop is difficult and expensive to repair. Unless you REALLY know what you are doing you could end up with a nice doorstop. One example is IBM. I recently got an old, old, compact Thinkpad called a 510cs. It uses the same barrel connector as the newer Thinkpads. Fortunately, I checked with my meter. Sure enough, THE POLARITY IS REVERSED between the 500/510 series and the newer Thinkpads. THAT would have been a mistake.

As long as you can verify the polarity is correct on the connector ('name's' problem) (this is usually shown at the socket), and the supplied voltage is correct then you can use a generic regulated power supply as long as it's capable of supplying the minumum 2.3Amps required (the wattage is purely a product of the voltage x current (15 x 2.3 = 34.5watts)). Apparatus will draw as only much current as it needs (so you can always go for a bigger current output) but you must not supply a higher voltage. "I know that I'm mad, I've always been mad"

johnr, your answer is correct as far as it goes, but my practical experience generally, on mismatched power supplies, has been different. Sometimes, a "generic" power supply might just not be very well regulated. Sometimes, a power supply that is marked x volts at y amps, may not ACTUALLY put out x volts. It might be somewhat higher (poor regulation) under a lighter load. I guess the point I was trying to make is, laptops are not lightbulbs. Lightbulbs are not very fussy on voltage, polarity, nor are they normally expensive to "fix." Therefore, I'd either stay with an original equipment power supply, or buy an aftermarket laptop power supply that is SO MARKED by the seller as meeting whatever specs you require. In other words, don't just putter down to the thrift store and buy some used wall wort. AND AGAIN, do not assume the polarity is correct. CHECK it with a meter. Some barrel connectors are - shell, some are + shell.