$10 was a mid-2009, finally got OS X Mavericks running today
Typing from my Mavericks desktop now

I don't really have any money so I use it to login to my bank

But that's a reasonable precaution. I completed my two month project of only using Mavericks and I've not stopped, it just sorta works fine!
recently snagged this 2006 iMac! I installed Snow Leopard 10.6.8
Its amazing how big the leap was from those first Intel ones! I have the same model on my desk but the older G5 from a year earlier and it physically groans (like it makes a creaking nose) when I ask it to play a video that I have specially encoded to work just right for it - and then look at yours going on modern youtube!
That's a lovely computer to do some web crafting on though, the screens are soft but they have a warmness to them that I really enjoy.
As for G4 power supplies, there are two kinds a bigger one and a smaller one and they both look the same but one is easy-ish to get (you can use a generic PC one) and the other one is IMPOSSIBLE to get unless you get an actual apple supply and they are silly money now. You should do some checking to see what on yours is (Id guess its the easier to find one).