For those three series, the only electrical difference is in the power ratings; that is, the number of watts that the adapter has been designed to provide. All three use the same 20VDC plug. My recommendation would be to standardize on a 90W unit. It will work for any of those systems (and more). The T60p requires 90W for best operation because of the ATI graphics. I believe that the X220 and X300 were specified with a 65W adapter. However, you can safely connect a 90W adapter to those laptops. All it means is that the adapter doesn't have to work as hard to provide power. Think of it this way: you have a choice of two engines for your car that basically cost the same and delivers the same performance. One has a redline at 4,000RPM, while the other has a 7,000RPM limit. Assume you constantly drive the car at 3,800RPM. Which engine would you choose? The one that is almost at the designated limit of reliability (4,000RPM)? Or the one which still has some headroom to operate (7,000RPM)? Power supplies are essentially the same.
Yes, the 90W units are probably going to be the "larger" ones. But they're not that much bigger over the 65W units.
X22 X24 X31 X41 X41T X60 X60s X61 X61s X200s X300 X301 Z60m Z61t Z61p 560 560Z 600 600E 600X T21 T22 T23 T41 T60p T410 T420 T520 R50 A21p A22p A31 A31p
NOTE: All links to PC-Doctor software hosted by me are dead. Files removed 8/28/12 by manufacturer's demand.