My old adapter input is 100-240 V and 0.6 Amps; output is 12V and 0.5 amps
My new adapter input is 90-270V and 0.7 amps; output is 12V and 1.5 amps
polarity matches
Is it safe to use? I know that output is OK, but what about the input? Is it required to be the same?
Your new adapter accepts a wider range of voltages than the old, so that's fine.
It uses 0.1 amps more current (maximum) than the old one, but that's also fine. It's expected, in fact, because the new one can output three times as much current than the old. (But since your old adapter was able to power your router, your new adapter will not actually use that much current in this application.)
Go ahead and use it.
More detail: Your wall outlet provides a certain voltage - typically near 120 volts in North America, 100 volts in Japan, 230 to 240 in most of the rest of the world. As long as that voltage is within the adapter's acceptable range, it's ok.
For example, if you lived in a 230 or 240 volt country then even if your adapter's input voltage was spec'd at "only" 220 to 250, that would be completely acceptable. Whether the adapter will also work in some other country does not affect your use.
