1200W is the max Power that comes out of ur PSU, and 88% eff means: if ur System is running at 1200W it would consume 1200/88% = 1363W. If it consumes 1050W then ur system runs at 924W (PSU -> MOBO...).
Is this true of all power supplies? When I check the specs for an Enermax 1350W supply, it shows a "peak power" rating, which is generally higher than the wattage rating of the supply (but within the efficiency). I couldn't find the same specs for my Corsair AX1200.
Basically, I'm looking to see what the peak power is for the AX1200, which should be at least 1500W since it is 80+ efficient.
No you are misunderstanding the specs.
Power rating is in DC load. Period. 1200W means it can handle 1200W of DC load (whatever that may be in AC due to inefficiency). The Peak power rating is also measuring DC load. Neither rating is in AC load. The difference between power rating & peak power rating is the power rating indicates what the powersupply can handle continuously and the peak power rating is what spikes the powersupply can handle briefly.
Assumming you trust manufacturer specs exactly (which you shouldn't) a 1200W power supply w/ 1500W peak power rating can handle a continuous 1200W load 24/7/365 (assuming you trust the manufacturer specs which you shouldn't) and @ 88% efficiency it would draw (1200/0.88) 1363W at the wall (AC). The same power supply can also briefly handle spikes up to 1500W and @ 88% efficiency it would draw (1500/0.88) 1704W at the wall (AC) when DC load spikes to 1500.Remember power supply is best loaded at 60% to 80% of continuous rating (not peak rating) because that is where efficiency is the highest.
Peak power rating refers to the power limit the supply can handle for brief periods of time.
Peak power rating is pretty much worthless spec.
Power supplies are rated by their SUSTAINED DC load rating.
Due to inefficiency power supplies will ALWAYS draw more AC then then DC load they are supplying.
AC load = ( DC load / efficiency)