Back-up software for OSX

I like Dropbox for this. I keep my files synced between my iMac, MacBook Pro and Windows 7 desktop without any effort or hassle. It literally just works perfectly in the background.

 

You could buy an original power charger from eBay.
Cheaper than "recommended price", and much better than some knockoffs.

 

Since the data using DropBox is synced between at least two computer and also stored online, it could count as backup.

If you need more, look at Time Machine (included with OS X) or CarbonCopyCloner or SuperDuper! and any external HDD.

Time Machine FAQ

To learn more about Mac OS X: Helpful Information for Any Mac User by GGJstudios​

 

I would suggest you not look for one program to do both the things you need. Ideally you need 2 things for two tasks:

Task 1 - Sync files with a windows PC
Task 2 - Backup files

I'm not going to suggest anything because the things mentioned above fit your needs. Dropbox is free (unless you want a lot of extra space) and Time Machine comes built onto your mac. Use Dropbox to sync files and time machine to back them up.

Basically, you won't find one program that can do both tasks perfectly but you do have access to a program for each task without any problem at all.