The Signature 850w has the lowest wattage rating of the three units being examined, and it should come as no surprise that its maximum load specifications are the lowest. At full load, the 12v lines combined can supply up to 65 amps. The 3.3v and 5v lines are approximately the same between the power supplies, except the capacity of the Toughpower is a little higher.
The maximum combined output of the four 12v lines in the UCP 900w can output 71 amps. All three power supplies each have four 12v lines.
Boasting the highest total wattage rating of the units, Thermaltake's Toughpower 1000w has the highest maximum current output specifications. The maximum combined output of the 12v lines is 82 amps.
The Signature, UCP and Toughpower units have the same standard ATX motherboard compatibility. Looking at the total number of Molex and SATA (not including floppy disk drive plugs), the amount moves up with total wattage specifications. The Antec model has 10 connectors of these types, the Cooler Master has 14, and the Thermaltake has 16. Antec's Signature and Cooler Master's UCP units have the necessary native connectors for multiple GPU setups that require up to 4 PCIe power connectors. Thermaltake's Toughpower unit has an additional pair of 6 and 8pin PCIe power connectors, which would allow it to physically support triple SLI. The Signature and UCP would require Molex to PCIe power adapters to support this.
The Cooler Master UCP 900w is fully non-modular. Antec's Signature 850w is semi-modular. Its non-modular cables are ones that are generally used anyway in most computer systems. The Thermaltake Toughpower CM 1000w however is almost fully modular. All of its power leads are modular except for its ATX motherboard power cables.