By Abdelrahman Saed — Senior Mobile Engineer. Last updated: 2026-08-10.
They are not competitors — they are layers. Supabase is your Postgres backend (auth, database, storage, realtime). PowerSync is a sync engine that mirrors subsets of that Postgres database into on-device SQLite so your Flutter app works fully offline and reconciles conflicts when connectivity returns.
At iStoria we use both together: Supabase as the source of truth in the cloud, PowerSync to keep each device's local Drift/SQLite database in sync. If you need true offline-first with conflict resolution, this is the stack. Supabase alone gives you realtime but not robust offline writes.
| Feature | PowerSync | Supabase |
|---|---|---|
| Role | Sync engine (Postgres ↔ SQLite) | Backend (Postgres, Auth, Storage) |
| Offline writes | First-class, queued + synced | Manual (you build the queue) |
| Conflict resolution | Built-in policies | DIY |
| Sync rules / partitioning | Yes (YAML DSL) | No (you filter in queries) |
| Realtime | Via local SQLite watch() | Websocket Realtime (online) |
| Source of truth | Postgres (Supabase or own) | Postgres |
| Conflict cost | Included | Your engineering time |
| Best with | Drift/sqflite on device | Own client (postgrest, realtime) |
| Together? | Yes — recommended | Yes — recommended |
Supabase is an open-source Firebase alternative: managed Postgres, Auth, Storage, Edge Functions, and Realtime (websockets). It is your server-side backend. Your canonical data lives in Postgres.
PowerSync is a sync service that sits between a Postgres database (Supabase or your own) and on-device SQLite. It defines sync rules (which rows each user/device should receive), watches the Postgres WAL, and pushes changes to devices; device writes are queued locally and pushed back up with conflict resolution.
They solve different problems and compose cleanly.
Supabase Realtime delivers changes to connected clients over websockets. That is online realtime, not offline-first. If the device loses connectivity, queued writes are your responsibility, and there is no built-in conflict resolution for concurrent edits. You can build it (a writes queue, logical clocks, merge logic) but you are engineering the sync layer yourself.
PowerSync exists precisely to provide that layer: deterministic local-first sync with a conflict-resolution policy and a sync-rules DSL for partitioning data per user.
PowerSync ships a Flutter client (powersync) that syncs into a local SQLite database — which Drift can wrap. So your architecture becomes:
Supabase Postgres ←→ PowerSync sync service ←→ on-device SQLite (Drift) ←→ BLoC/UIReads and writes go to local SQLite (instant, offline-capable). PowerSync reconciles in the background. The UI never blocks on network.
You need PowerSync (or equivalent) when:
You do not need PowerSync when the app is online-only or can tolerate simple last-write-wins with your own queue.
// 1. Supabase backend
final supabase = Supabase.instance.client;
// 2. PowerSync client syncing into local SQLite
final powerSync = PowerSyncDatabase(
schema: AppSchema(),
path: 'app.db',
);
await powerSync.initialize();
// 3. connect sync with auth from Supabase
await supabase.auth.signInWithPassword(email, password);
powerSync.connect(async () => await fetchSupabaseToken());
// 4. read/write local — offline-capable, instant
final rows = await powerSync.execute('SELECT * FROM tasks WHERE owner = ?', [userId]);
await powerSync.execute('INSERT INTO tasks (id, title) VALUES (?, ?)', [id, title]);
// PowerSync pushes the insert upstream when onlinefinal supabase = Supabase.instance.client;
// online realtime — breaks when offline
final sub = supabase.from('tasks').stream(primaryKeyKey: ['id']).listen((rows) {
// update UI
});
// write — fails or is lost if offline unless you queue it yourself
await supabase.from('tasks').insert({'title': title});The PowerSync version gives you offline writes, sync rules, and conflict resolution out of the box. The Supabase-only version leaves offline behavior entirely to you.
Choose PowerSync when: the app must work offline-first with writes that reconcile on reconnect, you need per-user data partitioning via sync rules, or you want conflict resolution without building it. Pair it with Supabase (or any Postgres) as the backend.
Choose Supabase (alone) when: the app is primarily online, realtime updates are sufficient, offline behavior is limited to read-caching, or you are willing to build your own write queue and conflict logic. Most apps start here and add PowerSync when offline writes become a real requirement.
You need a Postgres database as the source of truth. Supabase is the most common choice because PowerSync has first-class Supabase integration, but you can use any Postgres. Supabase also gives you Auth, Storage, and Edge Functions that pair naturally.
No — Supabase Realtime is an online websocket stream. It does not queue offline writes or resolve conflicts. If you need offline-first writes, you need a sync layer like PowerSync (or you build one yourself).
PowerSync applies a deterministic conflict resolution policy on the server side when concurrent writes reconcile. You define sync rules in YAML to control which rows each client receives. For app-level merge semantics (e.g. field-level merge), you handle that in your write logic or Postgres triggers.
On a healthy connection, a local write typically syncs upstream within seconds — PowerSync queues the change and pushes it on the next sync cycle. The key point is that the UI never waits: the write is committed locally and is immediately visible to the user. If the device is offline, the change sits in the local upload queue and reconciles automatically when connectivity returns. You design the UX around 'write is instant, sync is eventual' — which is the entire premise of local-first.
Available for hire. Abdelrahman Saed is a Senior Mobile Engineer (Flutter) — open to full-time, fractional, contract, or advisory work. Hire me →
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