what's the most significant difference between ryzen 5 3500u vs 3550h because the specs looks same
Looks like the H is 35W and the U is 15W.
You can compare the two APU Specs from here:
Ryzen 5 3500u: AMD Ryzen 5 3500U | TechPowerUp CPU Database
Ryzen 5 3550h: AMD Ryzen 5 3550H | TechPowerUp CPU Database
Retrieving data ...