I recently just purchased a new condenser microphone . I wasn't sure if I should just buy the Nady SMPS 1 channel power supply or just save up and just get a usb audio interface ?
If you want to use the mic to record audio into a computer, get a proper interface, which these days will probably be USB. Choose one that supplies phantom power. The mic input on a computer is designed for the sort of headset mic you'd use for Skype calls etc. It isn't electrically compatible with a recording mic.
You are pretty certain to outgrow a 1 channel power supply since most stuff you want to plug a condenser mic into with convincing results can power it anyway. So it's more of a stopgap device.
Of course, with a USB (or other) interface you also put down a wad of money for a particular quality you are then tied into.
My own approach would be to get a good small analog mixer, probably a used one for its resale value. That is likely part of solutions with the largest cable mess and footprint, but it's a pretty versatile component you can use for other purposes and, if you ultimately have nothing else to do with it, you can hook it up to your stereo.
It's not clear just what you bought that condenser microphone for and whether the microphone itself was a reasonable choice for what you ultimately want to be doing (and paying for). If you are thinking about getting a USB audio interface, it seems you only want to get stuff into your computer rather than use it live, and then a handheld recorder with built-in electret condenser capsules might be the easier choice: as long as you are not investing into good preamps, you are not likely going to beat its noise level anyway, condenser mic or not.
So the main question is: what do you expect to do with your mic ultimately? And then figure out how to proceed to there in the best manner. Even if it may involve swapping the already acquired mic for something else.
These two things traditionally don't achieve the same goals; but most audio interfaces allow you to use phantom power (usually with a wall-wart adapter). One is for powering a microphone (for use live, radio, anytime a microphone is needed, etc.) and the other is for recording input from a microphone.
If you get a USB audio interface you'll kill a few birds with one stone, versus only getting phantom power out of a 1 channel power supply. With an interface that supports phantom power you're able to get an audio interface and power out of the same unit.
Plus, assuming you will be recording more in the future, that one interface can network up with others to provide you multiple inputs for multi-track recording.
Some USB interfaces that do provide phantom power (like this) cost not much more than your phantom power source. I think the overall quality may be better than using just a phantom power source and the built-in audio interface of your computer.
If it is not a computer where you want to plug in your mic, check if it does not provide phantom power on its own.