Problems with たつもり　and -ているつもり


So, my textbook just taught me about -たつもり and -ているつもり, stuff like this:
あの人は、全知があったつもりで話している。 => That person talks as if she had omniscience.

The "as if" pattern was introduced as a pattern for translation by my
textbook, but I already run into trouble using it on the exercises in it. See
here for example:

A:「つもり貯金」って何ですか。 B: 欲しい物があっても買わないで、それを **買ったつもり** で貯金することです。

First, I already have trouble with つもり貯金, I dont really know how to translate
it. However the main issue here is that I can't see how I should translate
this with the "as if" pattern. Other constructions which carry the subjunctive
mood also don't really work here in my opinion.

I usually would translate it like this:

A: (To save money(?)) what is this? B: Even though you wish to have a thing,
you don't buy it, and you save money **with the intention to buy it**.

I'd also like to point out that two other questions of mine ripple into this
one here: 1. Concerning -ないで [difference between -なくて and
-ないで](https://japanese.stackexchange.com/questions/48065/difference-
between-%e3%81%aa%e3%81%8f%e3%81%a6-and-%e3%81%aa%e3%81%84%e3%81%a7) 2.
Concerning つもり **で** [what is this で in this
sentence](https://japanese.stackexchange.com/questions/47990/what-is-
this-%e3%81%a7-in-this-sentence/48006#48006)

My translation is based on what I got from my second question linked here.




"With the intention to buy it" would be 買うつもりで. Since the example is 買ったつもりで,
it means "with imagination as if you had bought it".

Incidentally, "as if she had omniscience" translates into （まるで）全知のつもりで or
全知であるかのように.

買った and …である indicate that the issue has been realized while 買う does that it
has not happened yet. That's the difference.

（全知 is not a substantial noun but a so called の adjective, so 全知があった doesn't
make sense apart from some philosophical expression. Imaginary conditional in
Japanese is not a particular category beside normal conditional.)

