Advise a laptop user on a replacement power supply. A user sent the following email message:

I have an older laptop PC that has a dead power adapter. I have tried to find a replacement on the Internet but cannot find an exact match. Is it OK to substitute a replacement adapter that is close to the original in voltage and amperage, or do they need to match exactly?

Research the answer to this question and write an email response. Are there other characteristics of laptop power adapters besides voltage and amperage that the user needs to be warned about?