> If you add an UBI but don't fundamentally change the way the system works it won't make a difference, companies will just adjust the prices accordingly because more money will be in consumer's pockets (the market is always right! right?).

If you assume prices work according to supply and demand, incorrect. The reason for this is that people also earn money from sources other than UBI.

To give an example, let's say I give every single person in the US, including children, $5. Will companies raise their prices accordingly? Maybe, but the difference in GDP is tiny. The difference in the purchasing power of the average 10 year old with no pocket money though, is vast, since they previously had $0 and now they have $5.

Similarly, UBI will probably result in price increases, but those will be less than the increase in purchasing power of those most in need of UBI.