7I96 error

7805 is a Linear voltage regulator, meaning it heats a lot so using big aluminium heatsinks is mandatory.
Also there are several versions of it, from 0.5 to 1.5A, most are 1A max.
It also has current limiting and thermal shutdown, so might be those are kicking in.
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Side note,
I have used and still use several Mesa boards powered by USB, had a 7i92 and a 7i77 for over a year working like that with no issues ever.
The issue is with USB ports on the PC, some are rated at 0.5A, some can do 2A easily, but the issues might mostly bee due to overcurrent protection kicking in, seen that happen even when plugging a high end gaming mouse on some older PC's.
DC-DC cheap converters are a hit-and-miss affair, i have some that work nicely for several years and i have 9 that i can not use as the 10'th i had decided it was prudent to go all out and send 32V to power some 5V relays. This was a buck-boost converter.
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Meanwell does have 5V supplies, and that would be the lowest quality i would use for Mesa, Delta is much better, then there are over 100$.
Till late i used original Samsung phone chargers, can not find them anymore. Do NOT use cheap chargers, never ever.
Original RPI power supplies should be good, but beware some are 5.3V and that is above the Mesa limit.

Nice, thanks for reporting back.