Have had a Dell Inspiron 1545 on the bench, with a few issues.
I managed to get the laptop to charge, then it started to report it didn't like the PSU and won't charge.
A bit of a google round and found that dell and may be other laptop manufactures powers upplies are a bitsmarter than I thought. The PSU sends an ID bit or other data to the laptop to say what type of Power Supply is fitted?
"The AC power adapter type cannot be determined. Your System will operate slower and the battery will not charge."
I tried another Dell psu and the message disappears.
The Dell laptop Power Supply plug has an outer and inner metal contact, but with a PIN in the middle which send ID DATA to teh Dell Laptop.