I answered the very same question some days ago. Here you can find it: http://www.italki.com/answers/question/89708.htm Hope you can find what you are looking for there. In any case I will try to make a little summary. As you said the litteral meaning is "however, but", but also to add emphasis on the sence of "request for something" at the end of an interrogative clause. I would not say it is synonim of hesitance, it is rather a polite form, which allows you not to ask things in a too direct or harsh manner. +小切手を現金にしたいんですけど。"I would like to cash the check-KEDO, [is it possible to do it here?/can I do it here?]" As you see the meaning of the main clause itself does not change. You can say 小切手を現金にしたいんです。けど makes it sound like "The reason is that/the fact is that I need to cash my check...", adding a nuance of suspension or waiting. +アメリカに送金したいんですが。The same happens here "The fact is that I would like to transfert money to US, [is it possible?]" です-が & です-けど are synonim constructions, indeed. as for your second example, you could say アメリカに送金したいんですけど。

In these examples it acts like a conjunction. It signifies that the preceding clause is leading up to a request or something. E.g: I want to send money to America, (is that alright?) or (what form should I use?) けど and が bring about that mood. They very often follow a ~たい clause.