Take a look at the small chip that’s on this laptop motherboard - on the left you should see an SL4GH Pentium III Coppermine 600MHz mobile BGA CPU (it’s upside down in this photo). Right next to it is an Intel 440ZX-100M northbridge, and directly under it you should see a chip labeled ADP3421.
That’s the Analog Device ADP3421 Geyserville/Speedstep power converter, and it is found on a generation of laptops from the likes of Toshiba (usually the Satellite consumer models), Sony (PCG-SR and some C1 machines) and IBM (Thinkpad A/T2 x series), typically around the PIII Coppermine era. This photo is from a Sony Vaio SR9k parts machine.
They are known to fail after a few years of use and are responsible for machines developing power faults (they would either not come back on, or won’t come back on unless it went through extended downtime). The chips are EOL and no known drop-in pin compatible replacements exist, and it is unknown whether any of the known stock are still good or not. Every time I strip down a period laptop and I spot that chip, I throw up in my mouth just a little.