The closest thing I could find to the verb [to] imply (at least in the way implied is used in this context) in my dictionary was adfirmō, -āre, -āvī, -ātum. In this case you'd want to use the passive perfect participle, adfirmātum plus the adverb nōn. As for the noun power, you have a number of options depending on what kind of power you're referring to:
- potestās, f.
- (strength) vīrēs, fpl.
- (excessive) potentia, f.
- (supreme) imperium nt.
- (divine) nūmen, nt.
- (legal) auctōritās, f.
The pairs for each participle-noun pair are as follows:
- nōn adfirmāta potestās or potestās nōn adfirmāta
- nōn adfirmātae vīrēs or vīrēs nōn adfirmātae
- nōn adfirmāta potentia or potentia nōn adfirmāta
- nōn adfirmātum imperium or imperium nōn adfirmātum
- nōn adfirmātum nūmen or nūmen nōn adfirmātum
- nōn adfirmāta auctōritās or auctōritās nōn adfirmāta
When all of these are translated literally, they come out to mean something along the lines of "[type of power] having not been stated" or "[type of power] not stated", which isn't perfect, but probably as close as you can get to the English idiom "implied power" with Latin.
If the phrase “implied power” is being used to describe power of a strictly legal kind, then the word auctōritās alone would suffice, since from a pragmatic standpoint, this would would have already meant “implied [legal] power” to a Roman.