The classifications in The Richter Scale of Cultures is not necessarily an in-order listing of power per se, although that usually is the case. Attributes like planetary government and non-aggressiveness are factored in.

Ratings higher than our own (N) are extremely speculative since more advanced beings and races are not always forthcoming about themselves and we usually have no way of covertly or openly studying them.

AA
Prehistoric Age (No Tools)
Alpha Carinae 2, Alpha Majoris 1, Bardakia, Berengaria 7, Dimorus 4, El-Adrel 4, No'Mat, Ruah 4, Surata 4

AS
Primitive Space Dwelling
Alpha Omicron System (Junior), Giant Amoeba, Nitrium Parasites from the Pelloris Asteroid Belt near Tessen 3, Ordek Nebula (Wogneers)

A
Stone Age
Altair 3, Gamma Trianguli 6 (Vaal), Hanson's Planet

AR
Primitive ( RESTRICTED - No contact permitted)
Tarchannen 3, Tarella, Taurus 2

B-
Agricultural Age
Malkus 9, Miramanee's Planet, Rousseau 5

B
Metal Age
Apella, Capella 4 , Sigma Draconis 6, Galvin 5, Malurians (before demise), Zeta Bootis 3 (Neural)

C-
Scientific Intelligence With No Tools
Janus 6, Tyrellia

C
Scientific Age
Barkon 4, Fendaus 5, Mintaka 3

D-
Pre-Industrialization
M-113 (before demise), Omega 4, Organian Society's Outward Appearance, Sigma Draconis 3

D
Steam Age
Argo, Brax, Canopus 2, Omicron 4, Rigel 7, Tartarus 5

D+
Electric Age
Landris 3, Minara 2 (before relocation), Mintonia, Rubicun 3 (Edo)

E-
Liquid Fuels Age
Kraus 4, Loren 3, Stakoron 2, Suvin 4

E
Atomic Age
Barzans, Deneb 4 (Bandi), Beta 3, Mordan 4, Sigma Iotia 2

F
Space Age
Alpha Carinae 5, Altec, Argelius 2, Balosnee 6, Brekka, Kea 4, Penthara 4, Sarona 7, Straleb, Talin 4, Theta 7, Turkana 4

F+
Conscientious Space Age
Halkans, Marejaretus 6, Norpin Colony, Tagus 3, Thalos 7, Tohvon 3

G
Fusion Age
Antica (Beta Renna System), Deneb 2, Drema 4, Gamma Vertis 4, Jaros 2, Ligon 2, Manu 3, Minos Corva, Nahmi 4, Niau, Ophiucus 3, Regula, Selay (Beta Renna System), Sigma Draconis 4, Solais 5, Thelka 4, Ventax 2, Xelata

H
Planet Age
892 4 (Magna Roma) , Angel One, Bre'el 4, Ekos, Elas, Kataan, Kenda 2, Krios, Malcor 3, Ornara, Phylos 2, Quadra Sigma 3, Relva 7, Rochani 3, Troyius, Vault Minor, Zeon

I
Star Age
Algolia, Altair 6, Antide 3, Barolia, Breen, Chalna, Corvan 2, Gamelan 5, Largo 5, Ligos 7, Miradorns , Pakleds, Pelleus 5, Pentaurus 5, Regulus 2, Rura Penthe

J
Expansion Age
Alcyones, Berellians, Brakas 5, Gault, Lysia, Mudor 5, Nausicaa, Ogus 2, Otar 2, Qualor 2, Sothis 3 (Sataarans), Shiralea 6, Styris 4, Tarsas 3, Tormen 5, Tyrus 7A, Valeria, Zibalia

K
Introversion Age
Acamar 3, Alpha Proxima 2, Beta Antares 4, Coridan, Epsilon Hydra 7, Gamaris 5, Mizar 2, Narendra 3, Nimbus 3, Peliar Zel, Persephone 5, Setlik 3, Vadris 3, Xanthras 3, Zytchin 3

K+
Enlightenment Age
15 Lyncis 2 (Cait), Bajor , Gaspar 7, Hoek 4, Hurkos 3, Kurl (before demise), Mariah 4, Mataline 2, Meles 2, Memory Alpha, Pacifica, Parliment, Risa, Sauria, Sirius 9, Valo 2, Valo 3, Wrigley's Pleasure Planet, Zeta Alpha 2

L
Power Age
Angosia 3, Beltane 9, Benzar, Devidia 2, Dopteria, Eminiar 7 , Epsilon Canaris 3, Lenaria, Mantilles, Mariposa, Melina 2, Midos 5, Milika 3, Morikin 7, Oceanus 4, Promelians, Rakhar, Rigel 2, Rutia 4, Tagra 4, Tarsus 4, Vendikar, Zadar 4

M
Ion Age
Alpha Cygnus 9, Ardana, Bilana 3, Catualla, Canopus 3, Dachlyds, Daran 5, Delos 4, Deneb 5, Gonal 4, Hurada 3, Kaelon 2, Kaldra 4, Krisa, Kostalain, Lemma 2, Makus 3, Menthars(before demise), Merak 2, Nehru Colony, Zaldor

MR
Ion Age ( RESTRICTED - No contact permitted)
Kavis Alpha 4 (Evolved Nanites), Ktaria, Mab-Bu 6 A, Moab 4, Rigel 8 (Orion), Sarthong 5, Tanuga 4, Velara 3

N-
Pre-Technocracy Age
Aurelia , Axanar, Beta Lankal, Beta Thoridar, Beta 6, Beth Delta 1, Bolarus 9, Cardassia , Edo (Edoans), Ferenginar, Kora 2, Malaya 4, Talaria, Tau Ceti 3 (Kaferia), Tiburon

N
Technocracy Age
61 Cygni 5 (Tellar) , Alpha Centauri, Alpha 3, Andor (Epsilon Indii 8) , Arvada 3, Babel, Benecia, Bersallis 3, Beta Agni 2, Boreth, Borka 6, Cygnet 12, Deneva, Earth , Gideon, Gornar , Haven, Klaestron 4, Marcos 12, Minos Korva, Q'onos (Klinzhai), Rigel 4, Rigel 5

NR
Technocracy Age ( RESTRICTED - No contact permitted)
Minos, Platonius, Remus, Romulus , Scalos, Sheliak Corporate, Tau Cygna 5, Tholia, Tilonus 4

N+
Civil Technocracy Age
Betazed , Caldonia, Chandra 5, Danula 2, Delb 2, Delta 4, Efrosia, El-Aurians, Icor 9, New Fabrina, Ramatis 3, Tamaria , Trill , Ullians, Vulcan , Yonada, Zakdor

N+PR
Civil Technocracy Age ( RESTRICTED - No physical contact permitted)
Gagarin 4, Torona 4

NS
Space Dwelling Civil Age
Beta Renna Cloud, Beta 12-A Entity, Calamarain, Crystaline Entity, Dikironium Cloud Entity, FGC-47 Entities, Gamma Canaris Entity (Companion), Space Jellyfish

O
Techno-Power Age
Bynaus, Cerebus 2, Legara 4, Medusa, Mudd, Sarpeidon (before demise), Vorgons (from the 27th century)

P
Super Techno-Power Age
Amusement Park Planet, Borg Collective , Dyson Sphere Builders, Iconia (before demise), Old Ones of Exo 3 (before demise), Rubicun 3 (Edo God), Sargon's Planet (before demise), Triacus (Epsilon Indii 4, before demise)

PS
Space Dwelling Super Techno-Power Age
Gomtuu (Tin Man), V'ger, "Whale" Probe

Q
Cloaking Age
Aldea

R
Exploratory Age
Cytherians, Tkon Empire (before demise), Makers (of androids on planet Mudd), Vians

S
Transformation Age
Antos 4, Daled 4

T
Illusory Age
Melkotia, Prakal 2

TR
Illusory Age ( RESTRICTED - No contact permitted)
Talos 4

U
Dimensional Age
Guardian of Forever, Tau Alpha C (Traveler), Triskelion (Providers)

V
Altering Age
Excalbia, Trelane of Gothos, Kelvans, Pollux 5 (Apollo - before demise), Pyris 7 beings (Korob & Sylvia)

W
Galactic Age
Bajoran Wormhole Entities (Prophets), Dowds, Kalandans, Metrons, Preservers

WR
Galactic ( RESTRICTED - No Contact Permitted)
Vagra 2 (Armus), Lactra 7

X-
Pre-Non-corporeal
Discarders of Armus, Zalkonians

X
Non-corporeal Age
Organians, Thasians, Koinonians, Zetarians

XX
Nigh Omnipotence Age
The Q Continuum