Switzerland does it and it seems to work pretty well.
Financial institutions report your wealth (to some extent), and the development of wealth is checked against your income, making tax evasion non-trivial. You could hide the money in a shoebox but you'll lose more in opportunity cost (missed investment gains) than you'll save on tax.
The other side of the coin though is that capital gains generally aren't taxed.
Mainly, I don't agree that "it is very difficult to tax wealth". It's basically a box "your wealth: <enter number here>" on the tax declaration, with an extra spreadsheet/list to fill out showing what the wealth consists of, plus proof (e.g. bank/stock account statements).
* except for household and personal common usage goods
Anyone can declare assets anywhere but if they're not taxed, or taxed very little, then inequality grows. So does Switzerland do this better or fairer than other countries?
It differs between cantons (states, kinda) and has progressive banding. Someone with 100k in wealth will pay maybe 100-200 or so. If you have 100 million CHF, in Geneva you would pay around 1 million per year in taxes on that wealth.
As the OP stated, it is global assets and wealth, so foreign/offshored investments still attract the tax. Plenty of people choose to be resident in Switzerland even with these taxes.
My understanding is that it's not very effective, because any foreign-held asset is pretty much hidden from Switzerland, unless there's an agreement with the country for this kind of information.
