I dont have the 550, i do have the 500w which im using in my Barton computer. (pic in the avatar) the 12v is rated 34A, but after measuring it with a Voltmeter i didnt belive that, my 12v on idle was being reported @ 12.36v which is high but perfect for overclocking. When on load tho i went down to 11.90v which is still really good but that kind of drop is really big. This was when testing in my PC in the sig which uses alot of 12v power with the a64 and 6800GT. I ran my system perfectly stable without locking up and oced just the same as my 550Antec. The 3.3v rails were solid @ 3.34v, the 5v were solid @ 5.05v.
My Antec550 the 12v stays @ 12.04v load or idle and since it had more stable voltage i put it in the PC in my sig, and gave my brother the Aspire. The Aspire is a really good psu with good looks and pretty decent voltages and for the money you cant beat it. I just didnt like the 12v going up and down that much.
If i was to give the Aspire a rank 1 through 10 i would give it an 8. My Antec550 i give a 10 cuss the voltages are 100% stable