The answer to the final part is that the misinterpretation of that 163 character probably isn't happening where you think. The communication with the printer is probably working just fine, and the reason it has printed that ú is because that's precisely what the computer has asked it to print. And the reason the computer asked it to print that is that the computer is under the impression that this is the right thing to print. The problem almost certain crept in well upstream of the printer. The most likely offender would be the process by which the bar's menu got loaded into the point of sale system.

Suppose, for example, that you can supply the point of sale system with, say, a CSV file listing the menu items, their prices, their categorisation, and any other information required. If the encoding of this file were misinterpreted, these phantom ú characters would creep into the system's database at that point. So while the system is perfectly capable of telling the printer to print a pound sign (as we can see it manages on the right) the reason it doesn't do that for the offending items on the left is that the system's internal data store genuinely thinks that the name of that item is "ú5 COCKTAIL" because the name was read in wrong while the system was being set up.