It's a classic case of "get what you paid for". Which, unfortunately, isn't always the way it works in the IT industry.
With power supplies though, it almost always is. The first thing to check on your twenty buck PSU, is that the numbers actually - er - match.
It's rated to deliver a certain power, but almost always the numbers on the sticker don't multiply to make that figure.
Power = Volts x Amperes
The sticker will list a bunch of different current (amperes) and voltage figures; work out the power for each, and add them all up.
Even for the name brand stuff, you'll probably have less than they advertised, but that's par for the course (unfortunately). If the difference is comparitively large, move on.
If not, and it's well in excess of what you'll likely need to supply your boxen, you'll probably be safe enough.
But don't expect a cheapo supply to last more 'n a year.
(Aside: Cart uses Tagan brand PSUs, because he's a
They're big, heavy, black, and modular. Like Jockfinn. Awww, yehhh...)