It was discovered, both during that and subsequent encounters, that their ships, in fact, possessed a hodgepodge of variously acquired technologies.
As in the case of the Mondor, where it was observed by the Enterprise's chief engineer, Geordi La Forge, that "half the systems on this ship [had] been stolen from Romulans, Jarada, Klingons, [and] just about anybody they ever came in contact with." (TNG: "Samaritan Snare")
By 2380, the Pakleds had stolen or acquired enough ship parts to be able to retrofit their ships into formidable foes. These ships contained components from such species as the Romulans, Klingons, Ferengi, Bajorans, and Arkonians.
According to the Enterprise-D sensors, during it's encounter with the Mondor, the ship had apparently suffered engineering problems, including total guidance system failure. Upon first viewing the ship Mondor, which was described as being "broken", La Forge, mused "their rubber band broke, right?"
In repairing the guidance system, La Forge explained that the ship's power needed to be rerouted through a specific venturi chamber before it could be channelled to the engine's coils. The repair further required the reconfiguration of a number of specific separators. (TNG: "Samaritan Snare")
The Mondor was determined to have "very limited armaments." Furthermore, the ship was outfitted with something "similar to Romulan shields," and otherwise beyond their technology. As such, ongoing scans indicated that the ship had "progressive weapons potential."
With the futher coerced assistance, La Forge was able to take that potential from something with "barely enough juice [...] to blow off a passing asteroid," to being "armed to the teeth," with the strength of photon torpedoes. (TNG: "Samaritan Snare")
Ships of the class
According to the script for "Samaritan Snare", this "Pakled ship" was described as "an unusual alien ship. Hardly aerodynamic, this craft appears to be something of a throwback when contrasted to the Enterprise."