Laptop power adapter wattage?

I have an IBM Thinkpad T42p. I bought a universal power adapter for it the other day, which advertises compatibility with the T-series. However, on the bottom of the laptop, its input power requirements are listed as 72W (4.5 amps at 16 volts), whereas the universal power adapter is only rated to produce a maximum of 65W.

Might this cause any problems for me, or will I just notice it in the form of slower battery charging when I’m using the computer?

There are higher-wattage universal power adapters being sold, but everyone seems to be sold out of them.

We have seen cases with our Thinkpads where low-wattage adaptors would indeed not be able to charge the batter with the laptop on, especially if attached to the docking station. However, we found that even the weakest would quite happily charge the battery whilst the machine was off or in suspend or hibernate. This didn’t effect all laptops in all cases, so YMMV, depending upon the specific laptop.