In your situation you don't need it. If they kept no tax , there can be no refund .
DA-1 is a form to claim back tax (sometimes partially) on bank interest or share dividents located in another country where tax was taken there "at source". It's not just for the USA, but a long list of countries, (but not all countries, only whose who have a double taxation treaty with CH).
So basically:
- if you have a bank account abroad (or share dividends)
- and the bank abroad kept tax on the interest or dividends "at source"
- and the tax treaty says you should only pay tax on the country you are living
- and there is no easy way to get this tax back (ie, there is no simple form to complete in the foreign country)
- then you can complete DA-1 and get a refund from the Swiss .
But the amount you get back is up to (max) the amount of corresponding tax in Switzerland.
So eg, if you have a bank account in say Australia, you earned interest and the australians kept 100 chf in tax, then you complete DA-1 and one of two things happen:
- if the tax in CH is 150 chf, you pay only 50 to the swiss (reduce by the amount the australians kept)
- if the tax in CH is less than 100 chf, they waive that and you pay nothing to the swiss.
So in practice you end up paying tax which is the maximum of what the tax would be in the two countries.
For small amounts of tax, i think under 50 CHF, to simplify, you can just reduce the interest by the tax and just write this down (no need for a DA-1). For larger anounts of foreign tax refund you need to complete DA-1 and have proof of the tax witheld abroad.
Of course, you also need to declare the interest/divident on the swiss tax and pay Swiss tax on it. This obligation remains , even if you dont ask for a refund via DA-1. So, for example, you cannot say: well the australians already took tax on the interest, so I don't need to declare it on the swiss tax form. You must do it, and (well, optionally) ask for a refund of the australian tax via DA-1.
PS: (your last question): It's only for withheld tax. It doesn't make sense for tax paid later (via a tax return) as in these cases there would never be an overpayment of tax. Actually, doing a tax return is a reason why you cannot use a DA-1, as in that case you can recover the foreing tax directly from the foreign tax authorities, without the need to involve the Swiss. Also, being an american, the tax treaty says between US-CH says that USA citizens can be taxed double so even if they witheld you could not claim it as a refund, as it was 'correctly' taken in the first place (ie, you owe it). But if I am not an american and don't live there so I don't have to pay any USA taxes, but I have a bank account in the USA or shares there, and the USA kept tax on the interest or dividents, then I can claim all of this tax back via DA-1.