Yes, you want a parallel connection. If you wired them in series, each would only get 2.5 volts (that's assuming fans with the same DC resistance).
Also, even though supposedly a single USB port can source 500 mA (a half-amp)
This *might* work, but the question(s) remains...
no number, but the biggest
Have you cleaned out the woolieboogers in your pooter ??
1) Why do you want to power it from a USB port?
2) Is this a laptop or desktop?
I don't think this is a very good idea from many angles..
1) It's a waste of a USB port.
2) Depending on the fan(s) you choose, you do run the risk of overloading the USB port's current capability.
3) Very few fans are spec'ed at 5 volts. Almost all PC-related fans are 12 volt. Most fans will actually run "ehh" well (and slow on 5 volts, but many won't start rotation.
4) This sounds like a "cobble-up" job to avoid getting into your case innards (f desktop PC) or trying to avoid buying a reasonable "Laptop Cooler"
5) "Just adding fans" isn't the whole answer. You need to insure reasonable airflow directions and such.
6) How are your soldering/electrical skills? You might just create a flaky monstrosity that's intermittent or shorts out, killing off a USB port. (Not a shock hazard, but still uncool!)
If this is a laptop, buy a laptop cooler pad thingie. They use special fans designed to run on 5 volts and at a very low current. I've seen them starting at around $30 USD, but those are pretty crude.
(no "screwdriver smiley"..dammit) If this is a desktop PC, just get your hands dirty. Open your case. You may find there's already places set up for additional fans (3-wire fans are better for this). It's also pretty much a "no-brainer" to connect them. Most fans already come wired to (best) plug into a 3 or 4 pin connector on your motherboard (reason for "best" is that the speed is monitored by the motherboard) as well as the (still OK) adapter to plug into an existing drive connector.
The existing additional mounting points are usually already in a good place for airflow considerations.
Still on the "whys"..
What makes you think you need extra cooling? Are you having actual problems? Just want to be "cool" (pun intended)? Had some friend tell you "you had to do this"?
I'm a firm believer in "If it ain't broke, don't fix it"
I've created more problems trying to fix "perceived problems that weren't" over the years than I care to count. Rough guess, well into the thousands.
Anyway, if you still *do* need added cooling, we need the usual "More Information"... Pleez rely...
Make/model of pooter, (details if homebuilt or 'obscure')
There's a huge number of PC cooling experts here on BP.Edit:
Edited to remove unnecessary quote. ~ tg