different brands..all do the same thing...exactly the same as clothes...you could buy clothes from like wallmart for really cheap, but if you wanna look cool u gotta get brand name clothes.
because power supplies have the dreaded 50 cycle hum and combine them with pedals that increase the gain (ex. distortion pedals) you are gonna get terrible hum. Once you plug that hum into a high-gain amp, all hell breaks loose. Hence people go for the quieter expensive power adapters. I have a Godlyke adapter and its very silent. But then, I dont use any distortion pedals...

Peavey 5150 head
Marshall 1936 Lead 2x12 Cab
'06 Jackson SLSMG
Dean Hardtail Select
ISP Decimator
Planet waves tuner
Weber Mini Mass
Ibanez Delay & Chorus

time is like a fuse; short and burning fast -- James Hetfield
then whatever

i use a Power COnditioner and i plus all my pedals through that, i have a variety of pedals that i use now, so they have different adapters, i put them through a power bar/extention and into my power conditioner, it keeps the power so fresh and so clean,

Gibson Les Paul Studio w/dirtyfingers pickups
Gibson Joan Jett Melody Maker
VOX ac30 head
Marshall 1960 4x12 cab
Fender Hot Rod Deville