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
According to AMD website, these 2 processors have the same part number YM3500C4T4MFG
Since the 2 processors have the same specifications besides the TDP, it may be possible that the same part is used for both, and the system UEFI is tuned to run the part at either 15W, in which case it identifies as 3500U; or at 35W, in which case it identifies as 3550H.
This could allow the notebook manufacturer to use the same part in multiple notebook designs, with different weights and cooling requirements. Note that this is my speculation, and I do not know if this is correct.
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