@King of the Wastes - I was going by the fact that I considered the current normal version of combat armor is the "light" variant while the reinforced versions were considered the "advanced" variant.
Powered Exoskeleton
Powered Exoskeletons existed a little over a decade before the Sino-American war. At first they were used by civilians and military personnel for jobs that may have been physically demanding such as loading cargo, disaster rescue, health care or even construction. The earliest versions worked on a slave-master system, the exoskeleton had to be attached to an external power supply in order to operate. Advancements in power cell technology eventually allowed a power pack to be attached to the exoskeleton so the wearer would be free from the slave-master system. It wasn't a perfect system as the exoskeleton required recharging by hooking up to a
recharge station after several hours of use however.
It wasn't until the military became involved a few years before the start of the Sino-American war when advancements were made to the exoskeletons. The military noted the benefit of making their soldiers stronger by wearing exoskeletons with their normal combat armors and gaining the ability to carry more equipment and the use of heavy weapons such as Miniguns and Gatling Lasers. The military redesigned the power pack to accept readily available Fission Batteries that could last up to ten hours of prolonged use. Further developments of the exoskeleton resulted in military-grade versions that augmented strength and agility even more than civilian models but at the cost of increased energy consumption. This prompted the military to develop further enhancements to the power pack as the extra weight from carrying Fission Batteries and the overall cost of Fission Batteries was too high. The power packs were soon able to accept the much lighter and more affordable Micro Fusion Cells for power.
Prototypes were developed where instead of the exoskeleton fitting over existing armor, the exoskeleton was produced with armor plating as part of the exoskeleton. The armor plates almost fully covered the torso but only a portion of the legs and arms. There was however no combat weave integrated with the exoskeleton, it had to be worn underneath. Preliminary field tests were positive but the higher-ups weren't entirely impressed with the predicted costs to deploy each powered exoskeleton unit. Also if a soldier wearing an exoskeleton was to fall on the battlefield it would have been a very expensive loss. One General spoke out during a meeting saying he wanted his soldiers to be tanks. That while the armored and powered exoskeleton concept could be effective it wouldn't provide enough protection to justify the cost of each unit.
The other high-ups agreed and a costly research and development program quickly began on a enclosed suit of power armor that would provide exceptional protection and increased strength with the exoskeleton as a base. Many exoskeletons, civilian and military-grade were unfortunately torn down and used for parts during the development process of this new power armor. During the first couple months of the Sino-American war the latest power armor prototype was ready, the T-45d power armor. While it wasn't as agile as the simpler armored and powered exoskeleton concept it did provide excellent protection and provided more strength for the user, it's what the high-ups wanted for power armor. T-45d power armor was then rushed into production and deployed into the field only a year later just in time for the Anchorage Reclamation.
The exoskeletons that were fortunate enough to not be torn down still had use in the areas they were initially designed for, physically demanded jobs. Military-grade versions were in use early in the war but were eventually phased out in favor of lighter, effective and far cheaper forms of combat armor.
While not an armor (except for perhaps a surviving concept model of the armored and power versions) exoskeletons could be worn over various types of armor to provide increased strength but without the need for wearing power armor.
EDIT: Should've have added this when I posted but here's a picture that inspired the armored exoskeleton concept.
http://media.militaryphotos.net/photos/albums/album112/acr.jpg